You know what a trigger is - something on a gun that makes the bullet shoot out. With asthma, a trigger is anything that brings on asthma symptoms, such as coughing, wheezing, and trouble breathing. Triggers can vary from person to person and from season to season. They also can change as a kid grows older. Some common triggers include colds, smoke, cold air, exercise, and anything that causes an allergic reaction, such as dust mites or pollen.