allergy asthma linkage

What is the connection between allergies and asthma? We asked James T. Li, M.D., a Mayo Clinic specialist in allergies, asthma and immunology.

Oasis: Who gets allergies?

Dr. Li: Some people have a tendency to develop a variety of allergies. The medical term for this tendency is atopy, and we call these individuals atopic. Atopy tends to run in families.

Oasis: Is atopy always inherited?

Dr. Li: That is a very complex question. There is clearly a genetic component, but the development of allergies is also determined by exposure to allergens during a person’s lifetime. Some people who don’t have a family history of atopy still develop allergies, and some people with a family history of atopy don’t develop allergies.

Oasis: What is the overlap between people with allergic rhinitis (hay fever) and those with asthma?

Dr. Li: Atopic people may have allergic rhinitis, they may have asthma triggered by allergies, and often they’ll have both. If you look at children with asthma, about 70 percent to 80 percent also have allergic reactions to common substances in the air such as pollen, mold, dust mites, animal dander and so on. When they inhale a substance that they are sensitive to, it can trigger an asthmatic reaction.

About 20 percent of children with asthma are not allergic to such things as pollens or molds. Their asthma may be turned on by other factors such as exercise, cold air or respiratory infection.

It’s estimated that 40 percent to 50 percent of adult asthmatics also have allergies. Often, this group has had asthma since childhood. About 50 percent to 60 percent of adult asthmatics do not have allergic triggers for their asthma.

Oasis: Not every child who has allergies will develop asthma?

Dr. Li: That’s right. Not every person, child or adult, who has allergic rhinitis will also have or develop asthma.

Oasis: Is sinusitis involved in any way in this link between allergic rhinitis and asthma?

Dr. Li: An indirect link between allergic rhinitis and asthma is that people with allergic rhinitis are at risk of developing sinusitis or other respiratory infections. In a person with allergic rhinitis who gets sinusitis, the sinusitis in turn can trigger a flare-up of asthma.

Oasis: In what ways is the management of allergies and asthma linked?

Dr. Li: That’s an area of intense interest. Basically, if a person has both allergic rhinitis and allergy-triggered asthma, then avoiding exposure to allergens can be beneficial for both problems. For example, if someone has pollen allergy, one of the things we’ll work on is eliminating pollen from the home by shutting windows and using ventilation systems and air filters. If someone’s allergic to dust mites, then taking measures to reduce dust mite exposure in the home would benefit both the allergic rhinitis and the allergic asthma.

In addition, a regimen of allergy shots is sometimes beneficial for people who have allergic rhinitis and allergic asthma. In many people, treatment with allergy shots will benefit both conditions.

But the area of more intensive interest is whether aggressively treating the allergic rhinitis will directly or indirectly improve the asthma. There is evidence that people who have both allergic rhinitis and asthma benefit from having appropriate and aggressive treatment of both conditions. Since available treatment for allergic rhinitis generally is both effective and safe, it’s important for these people not only to have good asthma care but to have allergic rhinitis and other respiratory allergies treated as well.

controlling exposure of mold allergies

James T. Li, M.D., a specialist in allergy, asthma and immunology at Mayo Clinic, answers questions about mold allergies.

Oasis: What are molds and how do they cause allergies?

Dr. Li: There are many different types of molds, which are fungi that can grow in almost every environment, both indoors and outdoors. Mold particles or spores become airborne like pollen. If someone who is sensitive to a mold, particularly an outdoor mold, inhales the mold spores or mold particles, it can cause either an asthmatic-type reaction or symptoms of allergic rhinitis (hay fever), or both. People who are especially sensitive can have more severe reactions to mold than those who have reactions to pollen. Some people with asthma who are also sensitive to mold are at a higher risk of fatal or near-fatal asthma attacks, especially on days with high mold counts.

Oasis: Are the mold and pollen seasons in North America somewhat close together?

Dr. Li: The outdoor mold season varies. It's not as well-defined as the pollen season. But basically it starts in spring and ends in late fall. Usually the worst months are June, July and August. The mold season is longer, sometimes year-round, in warmer climates.

Oasis: Are there allergy problems with both outdoor and indoor molds?

Dr. Li: Yes, molds can be an indoor problem, particularly in damp environments. If you have a damp basement, it certainly can be a place where molds can thrive. Indoor molds and dust mites often go together. If you have a home with high indoor humidity, dampness and a musty odor, it's also likely to have dust mites and molds that can cause allergy symptoms in sensitive people. In addition, the spores from outdoor molds can enter indoor environments through open windows and doors.

Oasis: As with pollen, is it difficult to control exposure to molds?

Dr. Li: Yes. During the summer months, there are mold spores and mold particles in the air. As long as you're outside there's really no easy way to avoid exposure to outdoor molds. It's possible to reduce the indoor concentrations of outdoor molds by closing windows and doors and running air conditioners. As far as indoor molds go, high humidity is usually the culprit. We advise people generally not to run humidifiers in the home for two reasons. First, by increasing the indoor humidity, you promote mold growth or dust mite proliferation. And second, humidifiers themselves, if they aren't clean, can be reservoirs for mold.

Oasis: What about dehumidifiers?

Dr. Li: Dehumidifiers usually don't cause a problem — if you clean them regularly. I think dehumidifiers may be of some benefit in reducing the indoor humidity. But if the home has a lot of indoor humidity, a dehumidifier probably is not enough to control the situation. Something more may have to be done, such as landscaping around the house (to promote proper drainage) or fixing water leaks.

Oasis: Can people be sensitive to some types of molds and not others?

Dr. Li: Yes. And that's an important issue in the management of mold allergies. There are so many different kinds of molds that we literally can't keep track of them all. We do have some understanding about some of the more common molds, but there are many types of molds which are probably important in causing allergies that we just don't understand very well.

The allergy skin test extracts (given to stimulate symptoms) that we have for molds aren't quite as accurate as those for pollen, dust mites and animals. Part of the reason is that there are just too many types of molds. In addition, allergy shot treatment for mold allergies isn't quite as effective as the allergy shots we have for pollen. That's all the more reason for people sensitive to molds to see their physician to have their allergies carefully reviewed and treated with proper medicines.

Oasis: What other things can people do to control indoor mold exposure besides closing windows and doors, running air conditioners and trying to control indoor humidity?

Dr. Li: The recommendations are similar to those to control dust mite allergies: Remove carpeting from the home, cover bedding with allergy-proof encasements, and make sure there's adequate ventilation.