Asthma is a condition that causes episodic breathing difficulties. These episodes are caused by narrowed and inflamed airways of the lungs. Asthma “flares” or “attacks” can be triggered by dust, pollutants, smoke, allergies, cold air, or infections.

What Is Asthma?

Several changes happen inside the airways in the lungs of people who have asthma. First, there is inflammation, or swelling, of the lining of the airways. Second, the swollen tissues make a thick, slippery substance called mucus*. Third, the muscles around the airways may squeeze tight, causing the airways to narrow. These three processes—inflammation, mucus production, and muscle constriction—combine to reduce the size (the diameter) of the airways. That makes it harder to breathe, like trying to blow air through a narrow straw. During an asthma attack, these changes get worse. The airways swell on the inside while they are being squeezed on the outside. At the same time, thick mucus plugs the smaller airways. The person may start to make whistling or hissing sounds with each breath. The person’s chest may also feel tight. In addition, the person may cough to try to clear the lungs.

What Are the Severities of Asthma?

Cases of asthma vary in severity. Some people may have only mild symptoms a few times per month, whereas others may have severe symptoms every day. Asthma is has four levels, depending on how severe each case is.

Mild intermittent A person with this type of asthma has daytime symptoms less than twice per week and nighttime symptoms less than twice per month. Attacks are brief and usually do not affect activities. Intermittent means the symptoms come and go.

Mild persistent A person with this type of asthma has mild symptoms more than twice per week, never more than once per day. Nighttime symptoms occur more than two times a month.

Moderate persistent A person with this type of asthma has symptoms every day and flare-ups more than twice per week. Nighttime symptoms occur more than once per week. When symptoms do occur, they can last for days and can make it hard for the sufferer to participate in certain activities.

Severe persistent A person with this type of severe asthma has symptoms throughout the day and night. The asthma makes it hard or impossible for a person to participate in many physical activities.

What Triggers Asthma?

People with asthma have what are sometimes called “sensitized” airways.
Everyday factors that cause little or no trouble for most people can sometimes cause people with asthma to have a flare-up or attack. These factors are known as asthma triggers. There are two main kinds of triggers: allergic and non-allergic triggers. An allergic trigger results from substances called allergens*, which trigger an allergy. Examples of allergens that may trigger asthma are pollens, molds, animal dander (small scales from fur or feathers), dust mites*, cockroaches, and certain foods and medicines.
Most of these allergy-causing substances enter the body through the air people breathe, but some are swallowed.

The second kind of asthma trigger is called an environmental or nonallergic trigger. It has nothing to do with an allergy but causes the same kind of reaction in the airways. Irritating substances in the air, such as tobacco smoke, wood smoke, fresh paint, cleaning products, perfumes, workplace chemicals, and air pollution can trigger or make asthma worse.
Other non-allergic triggers include cold air, sudden changes in air temperature, exercise, heartburn, and infections of the airways, such as a cold or the flu. Exactly which of these might trigger a reaction varies fromperson to person.