Allergies are an overreaction of the body's immune system to foreign substances called allergens.

Allergic reactions can result in sneezing, coughing, runny nose, and itching. Most of the time the reactions are bothersome, but in some cases, they can be life-threatening and severe. Allergies may be seasonal, such as hay fever, but they may also be associated with chronic conditions such as asthma or sinusitis.