H1 blockers, also known as H1 antihistamines, are a class of medications that help relieve allergy symptoms. They work by blocking the action of histamine, a substance in the body that causes allergic reactions, such as sneezing, itching, and runny nose. Common examples include diphenhydramine and loratadine. These medications are often used to treat conditions like hay fever, hives, and other allergic reactions. H1 blockers can be classified into two categories: first-generation, which may cause drowsiness, and second-generation, which are less likely to cause sedation. Always consult a healthcare professional before use.