Histamines are chemicals that the immune system produces and release to send messages between different cells. They are mainly known for their role in causing allergy symptoms, such as a runny nose or sneezing. Histamines act like bouncers at a club, helping the body get rid of something thats bothering it, such as an allergen. When a person is allergic to a particular substance, the immune system mistakenly believes that this usually harmless substance is actually harmful to the body. In an attempt to protect the body, the immune system starts a chain reaction that prompts some of the bodys cells to release histamine and other chemicals into the bloodstream. The histamine then acts on a persons eyes, nose, throat, lungs, skin, or gastrointestinal tract, causing allergy symptoms. Histamines are also involved in local immune responses communication, as well as regulating physiological functions in the gut and acting as a neurotransmitter for the brain, spinal cord, and uterus. Histamines play a central role in several allergic conditions, including atopic dermatitis, contact dermatitis, allergic rhinitis, and allergic asthma.