Histamine receptors are specialized proteins found on the surface of cells that respond to the chemical histamine. There are four main types of histamine receptors, labeled H1, H2, H3, and H4. Each type plays a different role in the body, influencing functions such as immune responses, gastric acid secretion, and neurotransmission. When histamine binds to these receptors, it triggers various physiological effects. For example, H1 receptors are involved in allergic reactions, while H2 receptors help regulate stomach acid. Understanding these receptors is crucial for developing medications, such as antihistamines, which block specific receptors to alleviate symptoms like allergies and acid reflux.