Asthma Caused By Allergies

In some people, an asthma episode is brought on by an allergy to something in the environment. Allergies occur when the body reacts to common harmless substances that normally don’t trigger a response in another person. These substances are called allergens.

In the person with allergic asthma, a flare-up of the airways can occur when the allergen is introduced to the body. At first, reactions may be very minor, barely noticeable. But repeated exposure gradually increases sensitivity.

In an allergic reaction, certain body cells release various chemicals. In an asthma attack brought on by an allergen, these chemicals irritate the already inflamed air passages and cause the reactions that make the airways narrow and breathing difficult.

Common things that can trigger allergic asthma include tiny particles in the air derived from:

  • House dust mites
  • Cockroaches
  • Mold (spores)
  • Plants (pollen)
  • Animals dander

House Dust Mites

House dust mites are extremely small organisms that live in dust and feed on skin cells that have been shed by people. Products of dust mites are a common cause of allergies. They look like very tiny insects but are actually distant cousins of spiders. House dust mites thrive in warm, damp climates and are commonly found in mattresses, pillows, bedding, carpets, and upholstered furniture.

How-To Information

Ways to reduce exposure to dust mites:

Dust mites cannot be entirely avoided. But you should aim to lessen your exposure to them, particularly in the bedroom:

  • Put plastic zippered covers on mattresses and pillows.
  • In the bedroom, move out anything that collects dust (including the carpet if possible) and avoid upholstered furniture and clutter.
  • Wash all bedding each week in hot water (at least 130ยบ F).
  • Linoleum, tile, and hardwood floors are best for minimizing both dust and dust mites.
  • If possible, try to have someone who does not have allergic asthma do the vacuuming when you are not in the bedroom.
  • Vacuuming will not get rid of mites, and in fact spreads them up into the air for several minutes before they settle again. Try to use a vacuum cleaner with a HEPA air filter (which stands for “high efficiency particle arresting”) or a double-layer collecting bag.
  • Keep the humidity in the room low, around 35% if possible (never over 50%), because high humidity encourages dust mite growth.
  • Curtains should be laundered often; it is better to avoid heavy curtains and use window coverings such as easy-to-clean blinds.


The dried-up body parts of dead cockroaches are a very potent stimulator of asthma in those allergic to them. Regular cockroach control is essential to good control of asthma for people allergic and exposed to them. This can be a particular problem in big cities.


Mold is the greenish, gray, or black material that grows in damp places. Molds or fungi release microscopic particles called spores for their reproduction. These spores can float through open windows into the house, especially on cool nights in the spring and fall. Asthma attacks may also be triggered by the type of mold that grows in the house.

How-To Information

Ways to reduce exposure to molds include:

  • The use of air conditioners and dehumidifiers to reduce humidity. (They must be cleaned often to prevent mold growth.)
  • Regular ventilation of the kitchen, bathroom, basement, and other damp areas of the house. (Exhaust fans in the kitchen and bathrooms work well.)
  • Cleaning out mold from damp places in the house such as shower stalls, and clearing out moldy objects from closets. Use a spray cleaner with a fungicide in it.
  • Keeping bedroom windows closed to keep out mold spores and pollen.
  • Keeping drainage from rain water away from the house, in order to decrease humidity in the basement.


Pollen are microscopic particles released by plants for their reproduction. Pollen is more a cause of hay fever than asthma. But there are some people with allergic asthma who clearly have problems with ragweed and other typical plant pollens that can cause a flare-up in their asthma.

Make note of whether your episodes of asthma are worse when the pollen count is high.

How-To Information

To prevent allergic reactions due to pollens:

  • Pay attention to the pollen count in your area. Whenever necessary, keep the windows shut.
  • Air conditioning can be very helpful in minimizing pollen entry into the house and in keeping the humidity down. But check with your doctor before purchasing expensive equipment.
  • On days of high mold and pollen counts, if you have been outside for a prolonged period, take a shower and wash your hair before bedtime (to get the pollen and mold out). Also, leave your outdoor clothes out of the bedroom.
  • Change pillowcases every two to three days.

Animal Hair And Dander

Many people are allergic to a substance in the saliva and on the skin of furry animals. This substance, called dander, is a powerful allergen. It gets on a dog’s or cat’s coat and is spread into the air and onto surfaces.

Dander can float through the air for hours. Cat allergen particles, for example, are only about one-tenth the size of dust mite allergen particles and can escape the filtration system on most vacuums. Cat dander can still be found in the dust of a house even months after a pet has left.

Hamsters, gerbils, mice, and rats can produce the same problem. In some individuals, fine particles on feathers may also set off an allergic reaction.

Nice To Know

Animal allergens are a potent stimulator of asthma. It is very likely that frequent asthma symptoms in someone living with a furry pet are caused by the pet.

How-To Information

To prevent allergic reactions due to exposure to animals:

  • The best way to deal with pet allergy is to find the pet another home.
  • If this is out of the question, the pet should be kept outdoors as much as possible and never allowed into the bedroom.
  • Frequent washing (twice weekly at least) of the pet may also reduce the presence of animal dander in the home. Dog washing does not present any major problems when animal shampoo and lukewarm water are used. Cats present a greater challenge but can be slowly accustomed to the ritual by associating a positive experience such as feeding with the bath. Shampoo is not needed nor is it necessary to immerse the cat in water. A gentle wiping with a damp cloth will help remove some of the cat dander.
  • Deciding what to do about a pet is not easy, but if its presence really worsens the asthma condition, making the hard decision is the right thing to do.

Need To Know

Do some foods cause asthma?

Foods are rarely implicated as a cause of regular asthma. Asthma in some people can be triggered by an allergy to certain foods, but the asthmatic symptoms are usually part of a serious reaction called anaphylaxis.


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