Leukotriene: One of a group of chemicals produced by the body that accompanies inflammation. Leukotrienes are believed to play a major role in causing the symptoms of hay fever and asthma. From Asthma and Allergy Resources Allergic asthma9 Things to Know About BenralizumabHow Asthma and Sinusitis Are Connected Featured Centers What Are the Best PsA Treatments for You?Understanding Biologics 10 Things People With Depression Wish You Knew