Histamine blockers, also known as antihistamines, are medications that help reduce the effects of histamine, a chemical in the body that plays a key role in allergic reactions. By blocking histamine receptors, these drugs can alleviate symptoms such as sneezing, itching, and runny nose caused by allergies or colds. There are two main types of histamine blockers: H1 blockers, which are commonly used for allergies, and H2 blockers, which are used to treat stomach issues like acid reflux. Both types work by preventing histamine from binding to its receptors, thus providing relief from various symptoms.