An antihistamine is a medicine for an allergy — that unpleasant reaction to pollen, dust, some foods, or a sting. Your body makes a chemical called histamine when it thinks something is a problem, and that is a big reason you sneeze, itch, or swell. An antihistamine does not kill the pollen or the food. It blocks histamine, so those feelings calm down. Doctors give it for hay fever, itchy skin, and some insect bites. Older kinds can make you sleepy; some people even take those at night on purpose. Newer kinds are made so you can stay awake. In everyday talk people often say allergy medicine, which is looser — that bag can also hold other drugs. Antihistamine is the more exact word, a bit more doctor-like, but still common on the box.