Hay fever, the common name for respiratory allergies, is your body's reaction to irritants in the air. Normally your immune system fights off only those things that threaten your health, such as cold viruses and cancer cells. But like a hypersensitive smoke detector, an allergic person's immune system sounds the alarm at the slightest provocation, sending off waves of the chemical histamine to fend off the presumed offender. Unfortunately, the side effects of histamine are the symptoms we associate with allergies: a runny nose and sneezing, itchy nose and throat, watery red eyes, and congestion.

About one person in ten suffers from allergies at some point in life. Allergies tend to run in families, women are slightly more likely to get them than men are, and they can start at any age.

Allergy attacks are usually triggered by such things as pollen, mold, animal dander, and -- gross! -- the microscopic waste products of the hordes of tiny dust mites that live in your bedding, carpets, furniture, and clothes.

Try keeping a diary of your symptoms. Track when and where you notice them, as well as what you were doing at the time. If you notice that your nose starts running every time you go down into your damp basement, for example, you've probably found your culprit: mould.

If that doesn't work, an allergy specialist can give you a skin test to find out what's setting off your immune system's alarm button. In this test, small amounts of allergens are either scratched or injected into your skin. If you're allergic, the area will become red and irritated. Skin tests are generally reliable, but they can sometimes yield false positives and negatives.

When the offending allergen goes away -- when pollen season ends, for example -- so will your symptoms. But if the culprit is the family cat, you'll need that box of tissues for a while.

Sometimes allergies do go away or become less severe over time, but they can also worsen as you get older. Many people get relief when they move to a new location, though they may develop a new set of allergies after the first few years (which is how long it can take for allergens in a new environment to trigger your immune system).

The best thing you can do is to try to avoid whatever you're allergic to. When that's not possible, these other strategies may work:

• Use antihistamines to stop itchy, watery eyes, a runny nose, sneezing, and a swollen throat or hives. These come in both prescription and over-the-counter pills, liquids, and injections. If your allergies are mild, an over-the-counter drug will probably do fine. If it makes you sleepy, ask your doctor about one of the newer prescription antihistamines that don't cause drowsiness.
  
  
• Take a decongestant -- available as tablets, liquids, and nasal sprays -- to relieve congestion. Be aware, though, that using sprays too often can lead to rebound congestion, meaning the symptoms worsen each time they return until the spray is actually treating symptoms it caused.
  
  
• If you have severe symptoms, check into desensitizing allergy shots. This treatment, which involves injecting increasing amounts of the allergen into your skin, can help your immune system gradually adjust to irritants in the air until you can tolerate ragweed season without so much as a sneeze.
  
  
• Shower or bathe at night to remove pollens or other allergens from your skin and hair.
  
  
• Install clean air filters in your home often, and bring a portable air filter to your office. Keeping windows shut and running an air conditioner can also help keep pesky pollens at bay.
  
  
• Eliminate problem foods. If some of your hay fever symptoms last all year, you may have a food allergy or sensitivity. To find out, stop eating milk, eggs, wheat, chocolate, corn, oranges, rye, and oats -- all foods that can bring on allergy symptoms -- for at least three weeks (three months in the case of milk) to see if your symptoms go away.
  
  
• If pets are causing your allergies and you can't bear to part with them, try keeping them outside -- or at least out of the bedroom, where you spend a third of your life. This will significantly reduce your exposure and ensure a good night's rest. Also, ask a nonallergic friend or family member to bathe your animals frequently, and dust and vacuum their favorite areas often.
  
  
• If dust mites are causing your agony, clean your mattresses, pillows, and upholstery regularly; these are favorite hiding places for mites. Put away that down comforter and consider getting a hypoallergenic pillow and encasing your mattress in plastic.
  
  
• Finally, keep your immune system healthy by managing stress, getting enough sleep, eating a healthful diet, and exercising regularly.