Allergy

Part of the immune system's role is to protect the body from infections from various microorganisms, but sometimes it overreacts to what is typically a harmless substance.  This overreaction is known as an allergic reaction.  Common airborne or inhalant allergens include pollen, dust, dust mite, mold, animal dander. The classic example of inhalant allergy is hayfever when people develop symptoms such as sneezing, nasal congestion, itchy eyes and asthma because of allergy to pollen.

Allergy symptoms are predominantly mediated by the release of histamine, hence, the use of antihistamines to treat allergy.  Allergic reactions also release numerous inflammatory mediators.  In essence, allergic reactions are inflammatory reactions.  All organ systems are susceptible to inflammation. 

Inflammation in the nose causes congestion; inflammation in the lungs-asthma; inflammation in the gut-"irritable bowel syndrome"; inflammation in the joints and muscles-arthritis and myalgia, in the brain-brain fog, memory impairment.