Allergies

An allergy is your body's reaction to a foreign substance--such as pollen or pet dander--that enters, or comes in contact with the body. It may be that pollen never bothered you before but over time, and with repeated exposures, your body grew overly sensitive to it, resulting in allergy symptoms such as sneezing and watery eyes. When foreign substances such as pollen cause allergic reactions, they are called allergens.

Allergens cause cells in your body to release chemicals known as mediators, which trigger allergy symptoms. These mediators include histamine and prostaglandins.

• Histamine is the mediator that stimulates mucus production and causes redness, swelling and inflammation.
• Prostaglandins are mediators that constrict airways and enlarge blood vessels.

• The Mechanism of an Allergic Reaction