Hay fever is an allergy to certain tree, grass and weed pollens. During hay fever season, symptoms can be close to unbearable at times, depending on the pollen count. Hay fever is triggered when you breathe in pollen that you're allergic to. Your immune system overreacts and thinks the pollen is dangerous, so it sends out an antibody called immunoglobulin E to neutralize the invading pollen. Among the tools your immune system uses to wage war against the allergen are many chemicals, including histamine. Histamine is responsible for most of the hay fever symptoms you recognize (and probably hate).
There are a few ways to treat hay fever. While the most obvious and most effective method is avoidance, it's not always the most practical. Instead, many people take medications to relieve their hay fever symptoms. Antihistamines work to block the histamine released by your immune system; some of the older types can make you a little drowsy, but the newer antihistamines won't. Antihistamines can be purchased over the counter or by prescription, typically in tablet form. You should take them daily, before you're exposed to the pollen that sets off your hay fever. Once an allergic response starts, it's usually too late to block the histamine.
Other drugs used to treat hay fever are decongestants and nasal corticosteroids. Decongestants are also typically taken in pill form and they work to unblock nasal passages. Decongestants are also available in nose sprays -- often mixed with antihistamines -- but they shouldn't be taken for more than a few days in a row. Otherwise, they end up doing more harm than good. But don't confuse decongestant nose sprays with steroid nose sprays, which reduce inflammation and can be used at a maintenance dose throughout hay fever season. Other types of treatments that require prescriptions are leukotriene receptor antagonists, which block certain chemicals responsible for mucous production, and allergy shots, which are administered for one to three years to desensitize your system to pollen.