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, gastroesophageal reflux disease (GERD), pollution, food, and secondhand smoke, the America Lung Association 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.