Your Home - The Allergens Within and How to Control Them

Allergic diseases caused by household allergens

Many people develop allergic reactions to allergens found within the home. These include allergens produced by house dust mites, domestic pets, such as cats and dogs, cockroaches and some types of fungus. Household allergens can cause a variety of allergic symptoms such as sneezing, nasal congestion and a runny nose (perennial rhinitis), wheezing, breathlessness and mild, moderate or severe asthma. In some cases, exposure to indoor allergens can also cause allergic skin disease also known as eczema (or atopic dermatitis).

Overall, approximately 20-30% of the population is allergic to one or more indoor allergens. Approximately 80% of children with asthma or nasal symptoms are allergic to indoor allergens. Asthma due to indoor allergens is a important clinical problem. Asthma accounts for approximately 1 out of every 7 visits of children to hospital emergency rooms. Some children may grow out of asthma by adolescence but in others the condition persists into adulthood.

Most people who become allergic to household allergens have a family history of allergy. They inherit the tendency to develop allergies and become allergic to allergens that they are exposed to in their living environment. Most commonly, these are household allergens, outdoor allergens (grass, tree and weed pollens; and fungi), and foods (milk, egg, peanut, fish etc.). Allergies to household allergens cause persistent ("year round") symptoms such as nasal congestion and asthma, whereas pollen allergens cause seasonal hay-fever symptoms.

The process of becoming allergic to indoor or outdoor allergens is the same. After being exposed to the allergen several times, the immune system of a person who is prone to develop allergies becomes sensitized. That is, it produces allergic antibodies (or IgE antibodies) against the allergen. These antibodies have special properties. They can attach to cells in the skin, lungs and nasal passages called mast cells. The allergic antibodies sit on the surface of mast cells. These cells contain small "bubble like" structures (known as granules) that are loaded with histamine and other chemicals that cause inflammation. When an allergic individual inhales the allergen, it is picked up by the IgE antibodies on mast cells. This causes the mast cells to release the granules containing histamine and the patient has allergy symptoms. This process occurs immediately when the allergen contacts the mast cell and that is why patients react rapidly to environmental allergens.

With pollen allergens, the symptoms go away after the pollen season, but in the case of household allergens, patients are continuously exposed year round. This results in persistent inflammation of the nose or lungs. This kind of inflammation is caused by other chemicals (called leukotrienes) and includes other cells (called eosinophils). Once inflamed, the lungs become supersensitive (or hyperreactive) and can react to other substances. This is the reason why asthma attacks can be triggered by virus infection, tobacco smoke, chemicals, stress or exercise. Becoming allergic to household allergens is one of the first steps in developing asthma. Once asthma develops the symptoms can be triggered by infection, other substances in the environment, and physical activity.

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How were household allergens discovered?

It had been known since the turn of the century that house dust made people allergic. What puzzled scientists was how could dust found in different people's houses, from different parts of the country, give similar kinds of allergic reactions? At first, it was thought that chemical reactions occurring in the dust produced "the house dust allergen". Scientists in the 1940's and 50's tried to isolate the allergen from vacuum cleaner bags of house dust!

This puzzle was finally solved in the 1960's when two Dutch scientists examined house dust samples under the microscope. They discovered that the dust contained lots of microscopic creatures, which were found to be house dust mites. The scientists (Drs. Voorhorst and Spieksma) found that allergic reactions were related to the numbers of mites in the house dust. Dutch patients had symptoms most commonly in the fall when there were large numbers of mites in their houses. Later, house dust mites were found in countries all over Europe, in the United States, Australia, Japan and all over the world. In all these countries, it was found that asthma patients were often allergic to house dust mites.

At about the same time that mites were discovered, an allergist working in New York found that several of his asthma patients were allergic to cockroaches. Similar patients were found in Boston, Chicago and other cities on the East coast. When cockroach allergen was blown into the patient's lungs in a allergy clinic, they developed asthma-like symptoms. To complete the story, it had been known since the 1920's that allergic reactions could be caused by animals such as cats, dogs, and horses. By the 1980's, it was clear that house dust allergen was biological, and not chemical, in origin. House dust allergy, therefore, is caused by biologic contaminants or pollutants in the home.

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Household allergies increase the risk of having asthma

Allergic reactions usually develop in early childhood. Typically, children first become allergic to foods such as milk and egg. In the second and third years of life, they begin to develop allergic reactions to indoor allergens and also to outdoor allergens, such as grass, tree and ragweed pollens. The reason why some individuals develop nasal symptoms whereas others develop asthma or skin diseases are not very well understood. Some people can develop an allergic reaction to indoor allergens and yet not have any clinical symptoms (they are asymptomatic). But many children and adults who develop asthma are more likely to have asthma if they make allergic reactions to indoor allergens.

Having the allergic reaction is a risk factor for asthma in the same way that high levels of cholesterol increase the risk of heart disease and smoking increases the risk of getting lung cancer. The risks of developing asthma if you are exposed to indoor allergens are comparable to these well known risk factors for other diseases. Therefore, it is important to try to reduce allergen levels in the home. First, to prevent people becoming allergic and, second, to reduce the symptoms of people who are already sensitive to the allergen.

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Allergens that may be present in your home

House dust mites:
House dust mites are 8 legged microscopic creatures that are closely related to spiders and ticks (they are not insects). The scientific order to which they belong is the Acari and the study of mites is called acarology.

Dust mites are about 1/3 of a millimeter long. They are barely visible to the naked eye but can be seen with a low power microscope. Mites develop from eggs through various larval stages and become adult at 20-30 days. Adult mites live for 8-10 weeks.

Courtesy of Dr. Euan Tovey, reproduced with permission

Dermatophagoides pteronyssinus

The main species of dust mites are called Dermatophagoides pteronyssinus (which means "skin eating feather mite") and Dermatophagoides farinae (the "flour mite," so called because it infests stored foods and grains). House dust mites are designed to live with humans. They feed mainly on human skin scales but can also feed on animal skin scales and debris found in dust. Humans shed approximately 5 grams of skin scales per week, which is enough to feed many thousands of mites! Mites thrive at temperatures 70-72°F and a relatively humidity of 75%. These warm humid conditions are exactly the same as those favored by most humans.

Courtesy of Dr. Euan Tovey, reproduced with permission

Dermatophagoides pteronyssinus

And guess what - mites love to sleep with you! Large populations of mites are found in beds, pillows, bedding (blankets, comforters etc.) and bedroom carpets. Even teddy and other soft toys are good homes for house dust mites. Fitted carpets and soft furnishings (sofas and chairs) are other common sites of mite infestation. Mites burrow down into carpet pile and into padded furniture. Carpets fitted onto concrete slabs in basements often become damp and harbor large numbers of mites.

To assess the level of mite infestation, acarologists count mites present in a house dust sample. A low level is less than 20 mites per gram of dust. Allergies develop when people are exposed to approximate 100 mites per gram (or more). Heavy mite infestation is greater than 500 mites per gram dust. Allergic individuals are likely to have symptoms if they are continually exposed to dust containing more than 500 mites/g. Some highly sensitive patients may have symptoms when exposed to dust with lower mite counts.

Approximately 90-95% of the mites found in house dust belong to the Dermatophagoides group. D. pteronyssinus prefers a more humid environment than D. farinae. In drier parts of the U.S., D. farinae predominates. These include areas such as Northeastern States and the Midwest (Ohio Valley). In moist humid areas, such as Washington State, the Southern States and Florida, one finds large numbers of D. pteronyssinus. From an allergic point of view both species produce similar allergens and both of these mites are used to diagnose and treat allergic reactions. There are two other species that are also found in house dust. Blomia tropicalis is found in tropical and subtropical areas of the world: Central and South America, Singapore and S.E. Asia. In the US, B. tropicalis is found in Florida, Texas and Southern California.

Courtesy of Dr. Enriquez Fernandez-Caldas, reproduced with permission

Blomia tropicalis

Another species that can also occur in house dust is Euroglyphyus maynei, which closely related to Dermatophagoides mites.

House dust mites themselves are too large to become airborne. They cannot be inhaled into the nose or into the lungs. However, mites produce many fecal particles that are about the same size as pollen grains. The feces are about 10 to 40 microns in diameter. During domestic activity, the fecal particles are disturbed, become airborne, and can be inhaled by people living in the home. When these particles enter the nose or the lungs, the allergens they contain are rapidly released.

Courtesy of Dr. Euan Tovey, reproduced with permission

fecal particles

Mites produce about 20-30 fecal particles a day and these can accumulate in large amounts in the home. Continuously inhaling small amounts of highly concentrated allergen may explain why mites cause asthma.

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Cockroaches

Cockroaches are arguably the oldest insects on the earth. Fossil records indicate that cockroaches were present from 30 million to 300 million years ago. They are highly adaptable insects and are found in many different environments on the earth. Cockroaches are well known as household pests. However, it is important to note that the main disease associated with cockroaches in houses is asthma. People living in cockroach infested houses frequently develop asthma. This is the main public health problem associated with cockroaches.

German cockroach Blattella germanica

There are over 50 cockroach species in the US, but the species that are most important in terms of allergy are the German cockroach (Blattella germanica) and the American cockroach (Periplaneta americana).

American cockroach Periplaneta Americana

Cockroach allergy occurs mainly among poor families living in low income housing, particularly in public housing projects, inner city apartments and tenement buildings. In the US, asthma has increased among people living in urban or inner city areas, who are more likely to live in housing that contains cockroaches. Over the past 10-20 years, the increase in asthma has occurred particularly among African American and Hispanic families living in this kind of housing. However, cockroach allergy is not confined to inner city areas, but occurs wherever substandard housing permits cockroach infestation. This can occur in low income neighborhoods in small towns and cities across the US, as well as in rural areas and communities. For example, trailer homes are often infested with cockroaches and rural single family homes can also become infested.

Cockroaches have a strong characteristic odor which is apparent in heavily infested houses. As with dust mites, cockroach allergens are secreted by cockroaches in the feces. Cockroaches also produce secretions that may contain allergens. Cockroach feces are larger than those produced by dust mites. The allergen could be inhaled as fragments of feces or as "flakes" of secretions. Cockroach secretions may become attached to dust particles, or may form small droplets that become airborne and are inhaled by individuals living in cockroach infested apartments.

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Cats, dogs and other furry pets

Most people know whether they are allergic to cats or dogs because if they go into houses that contain these pets they have allergy symptoms. The cat allergen is produced in the sebaceous glands of cat skin and in saliva. This allergen becomes coated onto the fur and is secreted by cats into the house in large quantities. Similarly, dog allergen is produced in saliva, becomes coated on the fur and is distributed around the house. There are approximately 55 million cats and the same number of dogs in the US Not surprisingly, it is difficult to avoid these allergens! Approximately 5% of the population is allergic to cats or dogs.

Other small furry mammals also cause allergic reactions. Rats and mice often cause allergic reactions in animal handlers working in laboratories. These reactions can be severe, and may require that the individual stop working with these animals because they develop asthma. House pets such as rabbits, guinea pigs and gerbils can occasionally cause allergies but cats and dogs are the most common cause of animal allergies. Cat and dog allergens are present on hair and skin flakes (or dander) and in furnishings. Large quantities of cat and dog allergens accumulate in the baskets, bedding and blankets used by the pets.

The amount of cat or dog allergen in the air can be very high and the allergen stays airborne for several hours. That is the reason why allergic patients have symptoms immediately on entering a house which contains a cat or dog. It has been estimated that a cat carries about 100 milligrams of allergen on its coat and sheds this allergen at a rate of about 0.1 milligram per day (a milligram is one thousandth of a gram). The allergen accumulates in carpets and sofas, on beds, in rugs and in chairs. The concentration of cat or dog allergen in dust from houses that contain cats or dogs ranges from 0.1 - 3 milligrams per gram of dust. To put these allergen levels in perspective, an allergic person can react to much less than one millionth of a gram of cat allergen present in the air.

Animal allergen contaminates the environment quite effectively. Cat allergen is regularly found in houses that do not contain cats. This suggests that the allergen is transported from house to house, most likely on people's clothes. There are certainly patients allergic to cats who have symptoms simply by sitting or standing next to someone who lives in a house with several cats. Reports of patients who developed cat allergy but who never kept a cat are quite common. These patients probably became allergic by visiting homes that contained cats or by being exposed to cat allergen in public places (schools, day nurseries, offices, etc.).

This makes avoidance of cat and, to a lesser extent, dog allergen quite difficult. For both cats and dogs, the allergen seems to be produced by many different strains and species. Patients often say that they do not get symptoms when they are exposed to their own cat, but do when they visit other houses which contain different cats. So far there is no scientific basis for explaining these kinds of observations.

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Molds and fungi

House dust from most homes contains mold or fungal spores. In damp houses, the spores germinate and the mold grows on walls, carpets and furnishings. Mold growth produces more spores which contaminate the air. Damp basements, kitchens and bathrooms are usual sites of mold growth.

Fewer people are allergic to mold than to other indoor allergens. In the US, the fungi that most often cause allergy are Alternaria, Cladosporium, Aspergillus and Penicillium. There are many other species that have been reported to cause allergies and allergists usually test patients using a mixture of molds. Alternaria sensitivity is common in arid regions of the country, such as the Midwest and desert regions of Arizona, Nevada, and California. Both Alternaria and Cladosporium occur at high levels in outdoor air and it is likely that most patients are sensitized following outdoor exposure.

Alternaria spores are large and elongated (about the same size as pollen grains), but most fungal spores are small and are readily breathed into the lungs. Allergic reactions to fungi usually cause rhinitis or asthma. Some fungi grow inside the lungs and cause other kinds of allergic diseases, such as aspergillosis, but this is rare. Infection of the sinuses by fungi can also occur and cause allergic fungal sinusitis, but again this condition is rare.

It is important to distinguish fungi that cause allergic reactions from fungi that may cause other illnesses. Fungi such as Stachybotrys produce certain kinds of toxins, but these species do not cause allergies. Allergies to fungi are complicated because there are many potential fungal allergens and different types of allergic and non-allergic symptoms. It may be difficult to decide which of the fungi present in the home cause the allergy. Your allergist can help answer these questions.

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Visiting your allergist

At the first visit with your allergist, the doctor will take a complete medical history with emphasis placed on your allergic symptoms. You can expect questions that will help the doctor determine the amount of your allergen exposure such as "Do you have any pets", "Which seasons cause your symptoms to worsen?" and "What medications have helped your symptoms in the past?"

After obtaining the history the physician will perform a physical exam. The doctor will pay special attention to your lungs if you have asthma, your nose if it constantly runs, and your eyes, ears, throat and skin, as these are common sites for allergic disease.

The next step will be to perform a number of skin tests to determine the allergens to which you are sensitive. This will include allergens such as dust mite, cat, tree and grass pollens, and molds. A positive reaction will look and feel like a mosquito bite and will last for approximately 15 minutes. Other simple blood tests may also be performed to help the doctor with the diagnosis.

If you suffer from asthma your doctor will likely have you perform a simple breathing test to see how well your lungs are functioning. This is a quick and painless test that provides the doctor with much information about your lungs.

At the end of the visit the doctor or nurse will sit with you to discuss how you might best avoid coming in contact with the allergens to which you are sensitive and will also discuss your options for treatment. These include allergen avoidance techniques, medications, and allergy shots. You and the physician will decide upon the best course of treatment for you.

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Environmental factors that affect indoor allergens

Today, we spend ~90% of our time indoors, either at home or in the workplace. This move towards a sedentary indoor lifestyle may contribute towards the increase in asthma seen in Western societies over the past 30 years. Allergy is the price we pay for this comfortable lifestyle. The changes that we have made to our homes to make them more comfortable also enhance allergen exposure.

Central heating, fitted carpets, and insulation maintain warm temperatures and high humidity, and reduce air ventilation. Humidity is one of the most important factors that affect mite growth. Reducing the relative humidity below 50% for 6 months of the year will kill dust mites. Unfortunately, most humans prefer more humid conditions. While it is possible to achieve low humidity in some parts of the US, (e.g. in the mountain states or deserts in the West) in other regions outdoor humidity stays high year round (in Florida, Texas and the Southern States).

High humidity causes mold growth and favors cockroach infestation. Even in areas of low humidity, indoor allergens other than dust mites are associated with asthma and allergic diseases. For example, at high altitude in Denver, Colorado and Los Alamos, New Mexico there are no dust mites, but the numbers of children with asthma are the same as elsewhere in the US Most of the children in those communities have asthma caused by cat and dog allergens. Mites can survive short periods of low humidity by "sealing" themselves off from the environment. They also burrow down into mattresses, carpet pile and furnishings where the local microclimate enables them to survive.

The use of central heating together with insulation of doors and windows has dramatically reduced ventilation of homes over the past 30 years. Most houses have less than 0.5 air exchanges per hour, which is not sufficient to permit removal of allergens from the air. This is a particular problem for animal allergy and enables cat and dog allergens to remain in the air for several hours. Paradoxically, federal animal health care standards require that cats and dogs housed in animal facilities of research institutes have 10 air exchanges per hour. This is similar to that found in hospital rooms. Yet most of us live in "tight" homes with at least 10 fold less air exchange than that considered necessary for optimal animal care!

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What makes an allergen an allergen?

Or put another way, what is it about mite feces, cockroach secretions and cat skin flakes that makes people have allergies? The property that these substances have in common is that they all contain allergenic proteins. Dust mite and cockroaches produce between 5 and 10 protein allergens. In several cases, the allergens are enzymes used by mites to help them digest food. They become allergens when excreted with the feces.

After being inhaled by humans, the allergens rapidly leach out of the feces and bind to allergic antibodies on mast cells. The allergenic proteins serve a useful function for mites, but cause misery for humans. Cats and dogs produce one or two important allergens whose function is not entirely clear. Most allergens present in pollens and foods are also proteins.

The "Allergens" graphic illustrates a simple scheme of what we know about allergens. The organism that produces the allergen generates a product that can become airborne (e.g. mite feces or cat skin flakes). The proteins present either inside or on the surface of airborne particle readily dissolve when they enter the nose and lungs. Allergic people produce a particular kind of immune response to these proteins that results in the production of allergic antibodies.

Scientists have isolated all the important protein allergens and in some cases know exactly what the allergens look like. The allergens can now be produced in the laboratory using biotechnology. In future, this will allow better allergy treatments to be developed.

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Measuring Allergens in the Home

Now that we know that indoor allergens are proteins, lets look at how scientists use those proteins to measure allergens in dust or air samples. You might ask "why we can't simply rely on mite counts or cockroaches caught in sticky traps?" The reason is that allergen levels can stay high "out of season" when mite (or cockroach) numbers are low. In practice, counting procedures are time consuming, require technical expertise and do not give us a precise handle on allergen levels.

By measuring allergen proteins, exposure to one allergen can be directly compared with another. We can also obtain more precise measurements and estimate what level of exposure causes allergies to develop, and what level causes symptoms to occur. Laboratory based tests have been developed for measuring the most important indoor allergen proteins. These include:

To assess allergen exposure in the home, a dust sample is collected from the bed, carpet or sofa. This is done by attaching a collection device to the vacuum cleaner and vacuuming a square yard area of the bed/carpet/sofa for 2 minutes. The dust sample is sent to the lab, sieved and suspended in saline solution. The dust extract can then be tested for allergen content.

The lab test is called an enzyme immunoassay or "ELISA" procedure. It uses specially prepared antibodies that detect only the mite, cat or cockroach allergen in the dust sample. These tests are sensitive and can measure minute quantities of allergen - as little as one billionth of a gram! The lab sends out the results in terms of micrograms of allergen per gram of dust (µg/g). Mite allergen levels of less than 0.5µg/g Der p 1 allergen are considered low; at about 2µg/g most allergies will start to develop (patients become sensitized); and above 10µg/g allergic patients are likely to have symptoms.

If your home contains less than 0.5µg/g of any allergen, it is unlikely that you will develop allergies. If you are allergic and your home contains more than 10µg/g of allergen, you should consider taking steps to reduce the allergen exposure. Discuss this with your allergist or family doctor. Having your dust allergen tested, will enable the doctor to determine whether your level of exposure is significant.

Several commercial laboratories now offer testing services for measuring indoor allergens. Enquire about these services with your doctor or with your local indoor air quality specialist. These tests can help you decide whether you need to spend money on allergen control procedures or products.

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Prevention Steps - Avoidance of Indoor Allergens

There are three options for the treatment of allergic diseases caused by indoor allergens: anti-asthma drugs; allergy "shots", also called allergen immunotherapy; and avoidance of the allergen. You should discuss with your allergist or family doctor which of these options is appropriate for you.

Avoidance of indoor allergens is recommended by the National Heart Lung and Blood Institute and by the American Academy of Allergy, Asthma & Immunology as the first step in treatment of asthma. The use of allergen avoidance to treat asthma dates back to the turn of the century, when Europeans were recommended to spend time in sanatoria in the Swiss and French Alps in order to convalesce from asthma.

These sanatoria, for example in Davos, Switzerland are still in use today. In Italy, children living in Po Valley spend several months in the fall and winter at a special school in Misourina in the Italian Alps in order to recover from asthma. Dust mites cannot survive in the low humidity at high altitude. Similarly, "mile high" cities in the US, such as Denver in the Colorado Rockies and Los Alamos in New Mexico, have low humidity and virtually no dust mites. Asthma patients who spend several months at high altitude have reduced inflammation of the lungs and their lung function improves. This is why doctors believe that allergen avoidance is an effective way of treating asthma.

We also know that asthma patients who are admitted to allergen free hospital rooms will improve over a period of several months. Clinical studies have shown that the lungs of asthma patients improve if allergen levels in the home are reduced. Two factors are essential for allergen avoidance to be successful. First, the procedures used need to be effective in reducing allergens levels in the home. Secondly, the avoidance procedures usually need to be carried out for several months in order to be most effective. Intermittent or superficial treatments usually do not work.

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Creating an Allergen Free Home

If you are a non-allergic person, you can happily live with dust mite, cat or dog allergens without experiencing any allergies. But lets consider the scenario if you are allergic and want to create an allergen free home. You should consider this if you or your partner is allergic, or if you already have an allergic child, or are thinking of having children. If one or other parent is allergic, there is a 30 to 50% chance that children in the family will become allergic and possibly develop asthma.

Another scenario, even if you are non-allergic, is if your home is regularly visited by friends or relatives who have allergies. In modern Western societies, where partners often live separately, or live apart as a result of divorce proceedings, it is not uncommon for parents and children to visit other homes for several days a week and to be exposed to any allergen present in those homes.

Four steps to create an allergen free home:

1. Reduce the relative humidity to below 50%. This is easier said than done. In temperate climates, humidity can be reduced using central air conditioning systems or dehumidifiers. In climates with high outdoor humidity year round, central air conditioning may help, but in most cases will not reduce the relative humidity below 50%.
   
   
2. Increase ventilation. This is particularly important for cat and dog allergens which have high airborne concentrations. Increasing the air exchange rate in your house up to 5 air exchanges per hour will significantly reduce exposure to these allergens.
   
   
3. Consider removing wall to wall carpets and replacing them with hardwood, vinyl or ceramic tile floors. Carpets are a tremendous reservoir of both dust mite and animal allergens. Animal allergens accumulate to levels that can be 100 fold higher in carpeted rooms than in non-carpeted rooms. Using a flooring system other than wall to wall carpets is an important part of allergen control. This does not mean that the living area has to be spartan or "carpet free". Throw rugs, runners, small oriental rugs and dhurries can be used for decorative purposes, especially if they are washable and cleaned regularly, or can be dry cleaned.
   
   
4. Wash bedding regularly. This is important for dust mite, cat and cockroach allergens. Ideally, the bedding should be washed weekly in hot water at a temperature of approximately 130°F.
   

The steps outlined above represent ideals that are best achieved if you are building a new home or moving into a home that you own. If you rent or lease property, it may be difficult to remove carpets or make changes to indoor humidity or ventilation. These steps may call for changes in lifestyle that may not be acceptable to all family members. Bearing these general allergen avoidance strategies in mind, let's look at some additional measures that can be used to control indoor allergens - what works and what does not.

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Tackling dust mites (see checklist #1)

The main focus of mite control procedures should be the bedroom - this is where we spend approximately 1/3 of our time and is where dust mites thrive. Modifying bedrooms is cost effective and of proven clinical benefit.

Mattresses, comforters and pillows should be covered with mite proof covers or "encasings". These used to be made of rather uncomfortable semi-permeable vinyl fabrics. Nowadays, covers made from comfortable, microfine cotton or breathable synthetic fabrics are available that prevent mites or their allergens from passing through. The important feature of these fabrics is that they have a pore size of 6 microns, which is too small for mites to get through. New mattresses should also be covered with encasings (it takes 3-9 months for mites to colonize a new mattress).

Feather pillows have lower mite allergen levels than synthetic pillows because they are made of more tightly woven fabric. Synthetic pillows should be covered with microfine encasings or washed regularly.

Washing bedding weekly in hot water (130°F) kills mites and gets rid of mite allergens. It is important to wash bedding, even if the mattress is covered. This is especially true for patients with eczema because they shed more skin scales (mite food) into the bed. Ideally, stuffed animals should be removed from the bedroom, but any remaining soft toys, animals or mascots should be washable and washed weekly. Heavy curtains should be replaced with blinds or light cotton drapes and soft furnishings should be replaced with wooden, plastic or vinyl furniture.

Where possible, carpets should be removed from bedrooms, as described above. If the carpet has to stay, it should be treated with acaricide (containing 3-5% benzyl benzoate). These chemicals are nontoxic but need to be applied to carpets once a month to be effective. Vacuum cleaning removes surface dust, but does not dramatically reduce mite numbers. Mites burrow into carpet pile and are difficult to remove.

Mite allergic patients should wear a disposable face mask while vacuum cleaning. Preferably a cleaner with 2-layer microfiltration bags should be used to prevent allergens being dispersed from the vacuum cleaner into the air.

The underlying theme of mite control in bedrooms should be to make the room similar to a "comfortable" hospital room. The same principles should be applied to other parts of the house. Carpets control and use of wooden, vinyl or plastic furnishings should be introduced if practicable.

Other options to consider are the effect of temperature on dust mites. Freezing kills dust mites and it has been shown that applying liquid nitrogen to beds or carpets is effective at killing mites. For most people using liquid nitrogen is impracticable. If you live in Northern states, leaving the mattress out overnight on a cold winters night to freeze it, will kill all the mites. Putting soft toys overnight in the freezer is also effective (wash them afterwards to remove allergen).

Alternatively, dry heat will kill mites. In dry climates, leaving carpets out in the hot sun for a day will kill mites. Another approach is to steam clean carpets, although this procedure has not been widely tested. Steam cleaning could be useful in removing mites and destroying heat sensitive allergens. On the other hand, if the process left the carpets damp, it would favor mite growth. Steam cleaning processes vary from one company to another. At present, we know that "dry" steam-cleaning using a Vaporjet 2400 causes significant (>5 fold) reductions in mite allergen over several weeks. However, "wet" steam-cleaning usually has only short term effects (one to two weeks) before allergen levels recover.

What does not work for mites: Air purifiers, room air cleaners, air ionizers, or air duct cleaning are not effective mite control procedures. Mite allergens are only transiently present in the air and are not found in most air duct systems. Acaricides or chemical sprays are not useful for treating furnishings because they do not penetrate far enough into the upholstery.

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The approach here is to reduce animal allergen that accumulates around the home and especially to reduce the airborne allergen. Having a cat or dog in the home means that there will almost always be allergen present in the air, especially if there is more than one pet in the house. Patients who are highly allergic to cats or dogs should seriously consider getting rid of the animals and choosing alternative pets. Such patients include those who experience persistent nasal symptoms, breathlessness, wheezing or asthma, or who have had to visit hospital emergency rooms, following contact with cats or dogs.

Discuss your symptoms with your allergist to see if removing the pet is the best option for you. If you decide to get rid of the pet, it may take several weeks or months to completely get rid of the animal allergen. This is best achieved by vacuuming regularly using a vacuum cleaner, with a high efficiency particulate air (HEPA) filter or a cleaner with 2-layer microfiltration bags. All bedding, carpets and soft furnishings should be washed or cleaned. Walls, floors and other surfaces should be washed with detergents to remove the allergen. Use of a HEPA filter room air cleaner is advisable for 1-2 months after removing the pets.

If you decide to keep the pet, there are several things you can do to reduce allergen exposure (see checklist). Keep the pet outdoors if practicable, remove wall to wall carpets, and use HEPA filter room air cleaners. Washing the cat or dog twice a week with a regular pet shampoo or water will reduce allergen on the pet, and in the air, but this must be done regularly. If washing the animal is not practicable (cats!), wiping the fur daily with a damp cloth may help. Bedding should be washed weekly along with any blankets used by the animals.

What does not work (or is unproven):

• Use of air ionizers or electrostatic devices.
• Air duct cleaning - animal allergens can accumulate at high levels in ducts, but most of the allergen (90%) is retained within the duct system and not returned to the room. This would suggest that duct cleaning is of limited value.
• Special shampoos marketed for animal allergy are no more beneficial than conventional pet shampoos.
• There are no known diets or treatments that can be given to cats or dogs to stop them producing allergen.

Alternative pets:
Replacing cats with other small furry pets such as rats, mice, rabbits, guinea pigs, hamsters, etc. may work for a short while, but eventually allergies to these pets may develop. Small animals produce allergen in their urine and if you are allergic to these pets it is best to change the bedding and litter in their cages regularly (preferably have someone else do this).

Chinchillas may be an exception to this rule. These animals naturally produce very little urine (their thick coats are designed to prevent water loss). Although chinchillas have been farmed extensively for their fur, there are only one or two reports of chinchilla allergy. So, these animals may be worth a try. Otherwise, the choice of "allergen free" pets is down to rather cold creatures - fish, amphibians, lizards, snakes and reptiles such as iguana. That is, unless you would like to consider pot bellied pigs!

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Roach control (see checklist #3)

The main approaches to controlling cockroaches are physical methods to reduce cockroach access to the home and the use of insecticides. Food should not be left around the kitchen and all foods scraps and waste should be properly disposed of. Water leaks from faucets, sinks and bath tubs should be repaired. Cracks and crevices that harbor roaches should be filled and caulked.

The most effective insecticides contain hydramethylnon, fipronil or abamectin. These are available in supermarkets and drug stores as bait traps and can be applied as gels by pest control companies. The chemicals are effective at killing roaches, but need to be followed up by thorough cleaning using disinfectants, and cleaners to remove dirt and grease, in order to get rid of the cockroach allergen. Consult your local pest control company or agricultural extension service on how best to control roaches in your own home.

If roaches infest your entire apartment building, it may be difficult to stop them getting into your apartment. Such cases should be referred to the local public health department.

The University of Florida Cooperative Extension Service has an excellent web site which gives detailed instructions on cockroach control. The site features least toxic methods of roach control and how to manage cockroaches in low income housing http://edis.ifas.ufl.edu/IG105.

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Molds

The main strategy to control indoor mold growth is to reduce the humidity. This is achieved by home repairs to prevent water access into the home and repairing leaking roofs, windows, gutters, drains and water system leaks. Damp or wet carpets should be dried and cleaned. Dehumidifiers can be used in basements and air exhaust fans should be installed in kitchens and bathrooms. Showers, bath tubs, tiles should be cleaned with bleach or other bathroom cleaning agents available in supermarkets. Check any indoor plants for signs of mold and limit the number of house plants.

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Summing up household allergen control

Reducing allergen levels in the home is an important part of allergy and asthma treatment. It helps to reduce inflammation of the nose and lungs and can reduce the amount of anti-asthma drugs needed to control allergy symptoms. You can create "allergen free" conditions in your home and still live comfortably. This may involve changes to your lifestyle to better accommodate your health care needs and those of your family.

It is important to realize that it may take several weeks or 1-2 months before you notice clinical improvement after beginning an allergen control program. That is the time it takes for the inflammatory processes to return to normal. The amount of time to recover will depend on your level of sensitivity to the allergen and how effectively home allergen levels are reduced.

Be wary about claims made by manufacturers of allergen control products, devices and services, concerning their effectiveness against allergens. Often these products and services have not been extensively tested for their effects on allergens. Mattress covers, vacuum cleaner bags and acaricides have been tested and shown to be effective for controlling for mite and cat allergens. For many other products, this is not the case. Ask the manufacturers, sales people or service providers what their claims are based on. Discuss the best approach to allergen control in your home with your doctor.

Some studies suggest that avoiding allergens in the first few years of life prevents the development of allergies and asthma. Large clinical trials are now being carried out to see if this is correct. If you are allergic and are planning to have children, it is prudent to seek counseling from your doctor, pediatrician or allergist on avoiding indoor allergens and allergenic foods early in life.

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New products and treatments on the horizon

Over the next few years, we can expect that more consumer friendly methods of assessing home allergens will be developed. We can also anticipate that knowledge of allergenic proteins will lead to improvements in allergy shots and immunotherapy. While lab based tests for allergens are ideal for researchers, they cannot be used by the consumer.

Indoor Biotechnologies has developed a new type of test that is designed similar to a pregnancy test and measures mite allergen in the home. This rapid test detects mite allergen in 10 minutes - it gives a red line if allergen is present, and the color can be compared with High, Medium and Low indicator lines printed on the test. The test comes together with a simple plastic dust collector to make the dust solution that is applied to the test.

Rapid tests are designed to enable consumers to screen several sites in their homes for allergen levels. The tests should help consumers make rational decisions about whether they have allergens present and whether they need to consider avoidance procedures.

Allergen proteins are now being produced using genetic engineering techniques. While still at the research stage, allergens produced by biotechnology will be used for more precise allergy diagnostic tests (especially blood tests) and for improving allergy shots. Allergens can now be engineered so that they have greatly reduced binding to allergic antibodies. Allergens can also be coupled to other chemicals that shift the immune response from one that causes allergic antibody production to one that does not.

Using either engineered allergens or chemically modified allergens, scientists hope to improve existing allergy vaccines and develop new vaccines that may even prevent the development of allergy.
Allergy and asthma are significant public health problems. The economic costs of asthma alone are estimated to be $12 billion per year. Improved environmental control and the prospects of new allergy vaccines could profoundly improve the health of our children and our quality of life.

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