Healthy Homes

Learn more about:

Visiting Your Allergist
Environmental Factors
Properties of Allergens
Measuring Allergens
Allergen Free Home

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 test, called a spirometry or pulmonary function test, is quick, painless and 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.

Environmental Factors

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 the air is exchanged 0.5 times in one 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 air exchanged 10 times in one 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!

Properties of Allergens

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.

Measuring Allergens

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.

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.


There are three options for the treatment of allergic diseases caused by indoor allergens: antihistamines; 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.

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 in one 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.  Cover mattress and pillows in mite proof coverings.

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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