Asthma is frequently the result of an allergic reaction. Allergy involves the body releasing chemical mediators, like histamine, that cause reactions or symptoms when an individual is exposed to a substance(s) such as pollen, cat, or mold to which he or she is allergic. 

Various parts of the body can be affected by allergy (nose, skin, gut, etc.), including the lungs. Asthma involves sensitive airways which react to allergens (allergic reaction), as well as other conditions, such as exercise, infections, or weather changes. 

Airways in the lungs NARROW due to muscles tightening around the airways, swelling inside of airways, and producing extra mucus making it difficult to breathe. Allergy is the most common asthma trigger.