Your online resource for allergy, hay fever, and sneezing relief.

An allergy is the body's hypersensitivity to substances in the environment, including pollen count. Allergic reactions and allergy symptoms range from skin allergy, mild itching, sneezing or eczema (inflamed, itchy skin), to severe hives, hay fever, wheezing, and shortness of breath. An extreme allergic reaction can result in anaphylactic shock; a life-threatening situation in which a person's airway swells shut and blood pressure drops.

Scientists believe allergies originated millions of years ago as a way for the human body to rid itself of parasites and invading worms. The body fights these and other invaders by producing an antibody called immunoglobulin E (IgE for short) in the intestines and lungs. Without modern parasites to fight, IgE reacts to other foreign substances in the body. IgE triggers immune cells to release a number of chemicals, one of which is histamine. Histamine produces hives, watery eyes, sneezing, and itching. The more a person is exposed to allergens, the more the body produces IgE; hence, allergies often get worse with age.

The most common symptom of seasonal allergies is allergic rhinitis, otherwise known as hay fever. Symptoms of allergic rhinitis closely mimic those of the common cold.

But there are differences. A cold runs its course in 7 to 10 days. Allergic rhinitis can drag on for weeks or months. Despite its nickname, "hay fever" does not cause fever. With a cold, nasal discharge may be thick and yellow. In allergies, it is generally thin and clear. An allergy is often accompanied by eye, skin or mouth itchiness and can often be traced to a specific trigger.

Q: My hay fever strikes every spring and fall. I sneeze, my eyes water, and my throat itches. How do I choose the best medicine for me?

A: For typical hay fever symptoms, three over-the-counter options can help: oral antihistamines, decongestants (both oral and nasal sprays), and a nasal spray containing cromolyn sodium.

Brands such as PediaCare, Robitussin, Comtrex, and Benadryl, as well as generic store brands, contain antihistamines, either chlorpheniramine or diphenhydramine. These drugs are effective for runny noses, sneezing, and itching, but can make you drowsy.

"If the OTC antihistamines are effective in relieving symptoms but are too sedating, a newer less sedating antihistamine can be obtained by prescription," says Linda Hu, M.D., a medical reviewer in FDA's division of OTC drugs. Antihistamines work on a runny nose, but not as well on a stuffy one, so many brands combine an antihistamine with a decongestant (for example, pseudoephedrine). Decongestants can also be found in fast-acting nasal sprays, but these may have a rebound effect and after about three days they'll make your nose even more congested. They are better used for a short-lived cold than an ongoing allergy. One nasal spray that doesn't cause a rebound effect is Nasalcrom (cromolyn sodium). This drug is helpful to prevent your symptoms if started a few days before the allergy season begins and taken continuously. It causes few side effects and will not make you drowsy.

Remember that it's the active ingredient that is important, and many products contain more than one. Read the labels to make sure you're not combining drugs with the same ingredients. Look at the ingredients in the drug product and choose the type of ingredient that will best treat the symptoms you have.

Q: My job requires a lot of driving. Is it safe to take an antihistamine in the morning before I go to work?

A: Probably not. Antihistamines may affect your ability to drive or use machinery even if you don't feel sleepy.

"Drowsiness is the most common side effect of antihistamines and may be a problem for users who need to remain alert," says Hu. "Also, alcohol should be avoided because it may increase the drowsiness caused by antihistamines. If you need to be alert, some prescription antihistamines are less sedating."

Q: I have emphysema and high blood pressure. Can I take an over-the-counter allergy medicine?

A: Antihistamines should not be used by anyone with breathing problems such as emphysema or bronchitis, anyone with glaucoma, by those taking sedatives or tranquilizers, or anyone with difficulty in urination unless directed by their doctors. These drugs dry up secretions and may cause urinary retention and drowsiness, according to Hu.

Antihistamines may also cause dryness of the mouth and eyes and blurred vision.

Decongestants, which are in many OTC allergy medicines, can raise blood pressure. Ask your doctor what, if anything, you can take. People with heart disease, thyroid disease, or diabetes should not use decongestants unless a doctor says it's OK. If you're taking a drug containing an MAO inhibitor (sometimes used to treat depression), never use a decongestant.

Q: I've tried every medicine on the shelves, and I'm still miserable each spring. What else can I do?

A: See your doctor. There may be prescription drugs that are more helpful to you, you may need allergy testing or shots, or your symptoms may be caused by something else entirely.

--R.D.W.