Who Gets Asthma?
Asthma is very common, affecting more than 26 million people in the United States, including almost 7 million children. No one knows for sure why some people have asthma and others don't. People who have family members with allergies or asthma are more likely to have asthma.
Asthma can occur at any age but is more common in children than adults. Heredity can play a role. In young children, boys are nearly twice as likely as girls to develop asthma, but this sex difference tends to disappear in older age groups. Obesity is a newly identified risk factor for asthma.
What causes asthma?
People generally think of asthma in terms of episodes or attacks. Actually, the asthmatic condition is always present, but symptoms may be dormant until "triggered" by an allergen, respiratory infection or cold weather. Other triggers may include aspirin, environmental irritants, physical exertion and, less commonly, food additives and preservatives.
Allergens are substances that cause no problem for a majority of people but which trigger an allergic reaction in susceptible individuals. Allergens are a major source of breathing problems in both children and adults. Common allergens include plant pollen (tree, grass and weed), dander from pets and other animals, house dust mites, cockroaches, molds and certain foods. When an allergic individual comes in contact with one of these allergens, a complicated series of events causes the body to release chemicals called mediators. These mediators often trigger asthma episodes.
Cold air, smoke, industrial chemicals, perfume and paint and gasoline fumes are all examples of environmental irritants that can provoke asthma. They probably trigger asthma symptoms by stimulating irritant receptors in the respiratory tract. These receptors, in turn, cause the muscles surrounding the airway to constrict, resulting in an asthma attack.
Viral respiratory infections are the leading cause of acute asthma attacks. Surprisingly, bacterial infections, with the exception of sinusitis, do not bring about asthma attacks. Some people with "heartburn" can have asthma symptoms when stomach acid backs up into the esophagus.
Aspirin and aspirin-containing products can trigger asthma attacks in susceptible individuals. Five percent of people with asthma experience a significant decrease in lung function after taking aspirin. Similar reactions can occur with other over-the-counter pain relievers such as ibuprofen. As a general rule, people with asthma should avoid these products.
Another type of prescription medication that can cause problems is the group of drugs called "beta-blockers," which often are prescribed for high blood pressure, glaucoma, migraine headaches and angina. Beta-blockers can cause airway constriction called bronchospasm, so it is important for asthma patients to consult a physician about the use of these medications.
Although food additives can trigger asthma, this is rare. The most common food trigger is sulfites, a preservative used in products such as frozen potatoes and some beers and wines.
What is the difference between allergic disease and asthma?
Asthma is inflammation and obstruction of airflow in the bronchial tubes. Allergies are just one of the factors that can trigger asthma attacks. Not all people with asthma are allergic, and there are many people who have allergies but do not have asthma.