Half the cases develop in childhood, according to the Asthma and Allergy Foundation of America (AAFA). Many cases vanish by adulthood, but they may come back later in life.

Although the type, frequency and severity of asthma symptoms vary from one child to the next, they are all related to difficulty in breathing, the AAFA says.

Other triggers include weather changes, medicines, gastro-esophageal reflux disease (GERD), pollution, food and second-hand smoke, the ALA says.

The National Heart, Lung and Blood Institute says you should take these steps to care for asthma even when symptoms don't exist.

It's important for good health that everyone get regular exercise. The best type of exercise for someone with asthma is swimming, or an activity that includes short break periods, according to the American College of Allergy, Asthma and Immunology. Some patients with asthma may be advised by their doctor to use an inhaled medication (like albuterol) prior to exercise.