What Is Asthma?
Definition | Symptoms | Who's at Risk?

Definition Asthma is a disease of the lungs, specifically of the airways, which become narrowed, inflamed, and choked with mucus. These airway changes cause the breathing problems that occur in asthma.

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Symptoms
An asthma attack makes breathing in or out very difficult. This is why the classic symptoms of an attack are wheezing, coughing, and shortness of breath. If airway obstruction is severe, an attack may prevent any physical exertion or may even lead to a breathing emergency. People with controlled asthma often have normal or close to normal lung function between attacks, with essentially normal breathing and no shortness of breath.

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Who's at Risk?
Asthma can occur in anyone at any time in life, from infancy to adulthood. In some children with asthma, the disease goes away as they enter adolescence or adulthood. Asthma is slightly more common in boys than girls and occurs in more Hispanic and black than white children. Medical research suggests that asthma has both genetic and environmental causes.

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next: Anatomy/Function

Anatomy/Function
Airway | Function

Airway During breathing, air comes in through the nose or mouth and enters the large windpipe, or trachea. The trachea divides into smaller airways, called bronchi, which branch out into even smaller airways, the bronchioles, which are spread throughout the lungs. These small airways end in sac-like structures called alveoli.

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Function These airways "work both ways," carrying oxygen into the lungs and transporting carbon dioxide and other gaseous wastes out. The exchange occurs in the alveoli, which absorb the oxygen into the body and release the gaseous wastes to be taken up into the lungs and breathed out.

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next: Causes of Asthma

Causes of Asthma
Airway Irritants | Bronchiole Narrowing, Mucus Buildup

Airway Irritants
Most asthma attacks start with an irritation of the bronchioles that triggers the airway-narrowing response. Common causes of this irritation include allergies and upper respiratory infections. However, asthma can also be caused by exercise, acid reflux disease, aspirin, and sulfites (found commonly in restaurant food and certain wines and beers).

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Bronchiole Narrowing, Mucus Buildup In asthma, when the bronchioles are exposed to an irritating substance, they respond by closing down or narrowing. This leaves much less room for the passage of air into the lungs. The irritated bronchioles also fill up with mucus, which is filled with immune cells that the body has released in an effort to get rid of the irritating substance. But instead, the mucus buildup leads to further bronchiole obstruction and narrowing. The bronchiole narrowing and mucus buildup cause the breathing difficulties of asthma, which can become a medical emergency requiring treatment in a hospital.

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next: Treatment

Treatment
Prevention and Treatment | Preventing an Asthma Attack | Treating an Asthma Attack | Research Continues

Prevention and Treatment
Therapy for asthma consists of medications designed to prevent an asthma attack as well as medications used to relieve symptoms once an attack has occurred. A person with asthma must be very careful to take the correct medication at the appropriate time and not mix them up -- for example, both prevention and relief medications for asthma may be supplied in inhalers. This is very important since some medications are useful only for attack prevention and do not work once an attack has occurred.

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Preventing an Asthma Attack
The first step in preventing asthma attacks involves identifying and avoiding substances known to trigger attacks in a particular person. Examples include pets, insects, dust and mold, cigarette smoke, feather pillows, down comforters, and shag rugs.

If these efforts don't work, and the person needs medication for asthma prevention, the physician may prescribe inhalers -- the mainstay of preventing asthma attacks -- and/or pills. Inhalers prescribed to prevent asthma attacks must be used every day and often 2-3 times a day.

Steroid inhalers prevent the inflammation that occurs in asthma, thus reducing the buildup of mucus that contributes to bronchiole obstruction. There are also non-steroid inhalers that decrease inflammation and help prevent attacks.

Long acting bronchodilator inhalers used to prevent narrowing of the bronchioles, such as Serevent, contain a drug that works to keep an attack from occurring when the person is exposed to an asthma "trigger" -- for example, an allergy-causing substance like animal dander. Important: This type of inhaler is not effective for treating an attack once it has occurred.

Pills are also used to prevent asthma attacks. Steroids can be given in the form of pills. Some people with severe asthma must take steroid pills every day for weeks or years to keep from having an attack. However, doctors try to avoid prescribing steroid pills due to their many side effects, such as weight gain and diabetes. The newest pills to prevent asthma attacks are called leukotriene inhibitors, such as Accolate, Singulair, and Zyflo. These medications may be used to decrease the dose -- and thus the side effects -- of steroid pills needed to prevent an attack. Leukotriene inhibitors can also be tried as a substitute for steroid inhalers, depending on the severity of the patient's asthma.

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Treating an Asthma Attack
Treatment of an attack involves opening constricted airways, stopping airway blockage and mucus buildup which has occurred. Because the airways can be severely narrowed and breathing difficulty often very serious, treatment may at times require that the person go to the hospital to receive 1) breathing treatments to reopen the bronchioles and 2) intravenous steroids to decrease the inflammation. Some people have to stay in the hospital after asthma attacks. If an attack is very severe, the person may need to be hooked up to a breathing machine until air once again flows freely in and out of the lungs.

A less serious asthma attack usually can be brought under control without hospital treatment. With less severe attacks treatment-type bronchodilators, which act much more quickly than the ones used to prevent an attack, usually opening the bronchioles within a few minutes.

Once an asthma attack is under control, the person may need to take steroid pills, usually for about a week, to decrease the intense bronchiole inflammation. (Using steroids for short periods doesn't carry the same risk of side effects as long-term steroid use does.) If a bacterial infection is part of the cause of the attack, the doctor may prescribe an antibiotic as well.

Important: During an asthma attack, the person should continue to take regularly prescribed medications unless the doctor instructs otherwise.

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Research Continues
Prevention and effective treatment of asthma are the subjects of ongoing and intensive medical research. As new discoveries are translated into useful therapies, products, and services, WebMD will incorporate these advances into its related programs.

If you or someone you love needs to know more about asthma, please consult a physician. If you need to find a physician, try our Find a Physician. For more information about asthma, visit our Asthma Condition Center.