H1 receptors are a type of histamine receptor found in various tissues throughout the body. They play a crucial role in mediating allergic reactions and regulating physiological functions such as gastric acid secretion and neurotransmission. When activated by histamine, H1 receptors can cause symptoms like itching, swelling, and increased mucus production. These receptors are primarily located in smooth muscle, endothelial cells, and the central nervous system. Antihistamines, which block H1 receptors, are commonly used to treat allergies and motion sickness. By inhibiting the action of histamine, these medications help alleviate symptoms associated with allergic responses.