Causes, risk factors

If other people in your family have asthma, you are more likely to develop it. Asthma is closely linked to allergies. Most, but not all, people with asthma have allergies.

Asthma affects people of all ages, but often starts in childhood and is more common in children than adults. More boys have asthma than girls, but in adulthood, more women have asthma than men.

The most common reason, or trigger, for an asthma attack is an upper respiratory virus or a cold. Exercise, allergens and irritants also can bring on asthma symptoms.

Common allergens include:

• animal dander (from skin, hair or feathers)
• dust mites
• mold
• pollen from trees and grasses

Common irritants include:

• air pollution
• cigarette smoke
• cold air or changes in weather
• strong odors from painting or cooking
• scented products
• strong emotional expression and stress
• exercise

Causes of asthma

Scientists do not yet know how to prevent asthma, but certain factors increase the chances of developing it, including:

• having a parent with asthma
• having atopic dermatitis, hayfever and food allergies
• pneumonia or a respiratory infection with the respiratory syncytial virus (RSV) during childhood
• smoking (If a mother smokes during pregnancy, her baby may be more likely to get asthma. Exposing children to secondhand smoke also increases the risk of developing asthma, and makes the condition worse.)
• obesity is linked to asthma and other breathing problems
• living in a large urban area, especially the inner city, which may increase exposure to pollutants