Avoiding allergens

How allergens trigger asthma

When you breathe in an allergen, your immune system overreacts because it thinks the allergen is dangerous. Your airways become inflamed and full of mucus. The muscles in your airways also tighten, the air passages get narrower and you have trouble breathing. It all happens very quickly.

About 30 percent to 50 percent of people with asthma get these symptoms again 6 to 10 hours after they breathe in an allergen. This is called a late reaction.[2] Some doctors call all asthma triggers allergens, but others group them into allergens and environmental factors.

• The most common allergens are droppings from dust mites, pollen and flakes of skin or hair from animals (dander).
• Environmental factors include smoke and air pollution.

How to avoid allergens

You can take these steps to avoid allergens. They may help keep your asthma under control.[3] [4]

• Keep away from the things that start your asthma attacks, such as pollen or animals.
• Make certain you wash your hands after touching things that trigger your asthma (a friend's dog or cat, for example).
• Keep your home as free from dust as you can. Clean frequently and avoid thick furnishings, such as big cushions. Try wood floors instead of rugs and carpets, especially in your bedroom.
• Use dustproof covers with zippers on your mattress and pillows.
• Wash bed linen at a high temperature to kill dust mites.
• Treat soft furnishings with chemicals that kill dust mites.
• If you have a lot of moisture (humidity) in the air in your house, use a dehumidifier to make the air less moist (dust mites like humid environments).
• Don't smoke. Avoid smoky places.
• Keep perfumes and other things with a strong smell out of your home.
• Open your windows regularly to air the rooms. But be certain to close the windows if exhaust fumes or smoke is coming in.
• Make sure you take your asthma medicines the way your doctor or nurse advises.

What the research tells us

There isn't much evidence that avoiding allergens can make your asthma better or stop you having a serious asthma attack.[1] But we found one good study that showed that children with asthma had fewer symptoms when allergens in their home were reduced.[1]

Nearly a thousand children with asthma took part in the research. They were from seven large cities in the United States. Researchers split the children into two groups. For one group, researchers tried to remove possible allergens from their bedrooms. The children had skin tests to see if they were allergic to dust mites, smoke, cockroaches, pets, rodents and mould. Their environment was then made safer by:

• Putting covers on mattresses and pillows to block allergens
• Vacuuming carpets and floors with a HEPA (high efficiency particulate air) filter
• Setting up a HEPA purifier in the child's bedroom if people in the house smoked, if there were pets or if the child was allergic to mould
• Having professional pest control if the child was exposed to and allergic to cockroaches.

The other group of children in the study had no changes made to their bedrooms. On average, children whose environment was made safer had 34 fewer days with wheezing than children who didn't avoid allergens during the two years of the study.

Researchers have also looked at avoiding certain allergens. One that has been well studied is tobacco smoke.

One review of studies found that pre-school children who were around smoke in their home had a 30 percent higher chance of getting asthma symptoms than children who weren't around smoke at home.[5]

Another study with 807 children found that children's asthma symptoms improved when their parents smoked less around them.[6]