Antihistamines are a class of medications used to counteract the effects of histamine. This chemical, which is produced by the body, can cause a number of symptoms including:

• Itching (pruritus)
• Sneezing
• Runny nose
• Watery eyes

Antihistamines are sometimes used to treat skin conditions, such as itchy rashes. In addition, antihistamines are the most commonly used form of allergy medication.

Antihistamines are used to interrupt a natural reaction in the body. As histamine flows through the body, it irritates nerve endings, causing itchiness. Antihistamines have a molecular structure that resembles that of histamine. They therefore block the cell receptors that would usually accept histamines. This essentially makes the histamine molecules into ships with nowhere to dock. With the effects of the histamines interrupted, the severity of itching and other symptoms is reduced.