Astelin is a medication belonging to a class of drugs referred to as antihistamines. This drug works to block the effects of histamine, a chemical responsible for some allergic reaction symptoms. In case there is an allergic reaction, the body through the immune system releases an inflammatory chemical, the histamine. This chemical causes the capillaries to dilate, muscles to contract smoothly, and gastric to be secreted. There is a misguided immune reaction, antihistamines work to stop the release of histamine. Astelin helps prevent symptoms experienced in an allergic reaction such as runny nose, sneezing, and itching.