Asthma is a disease that can vary in severity from person to person. These are the four levels of asthma severity, according to the National Heart, Lung and Blood Institute:

• Mild intermittent asthma. Asthma symptoms come and go, occurring no more than twice a week. Symptoms occur at night no more than twice a month. Between asthma attacks, you have no symptoms.

• Mild persistent asthma. Symptoms occur more than twice a week but no more than once a day. Symptoms at night occur more than twice a month. Asthma attacks may affect your daily activities.

• Moderate persistent asthma. Symptoms occur daily, and nighttime symptoms occur more than once a week. Asthma attacks may affect your daily activities.

• Severe persistent asthma. Symptoms occur throughout the day and frequently during the night. Your daily activities are limited because of your symptoms.