Or you have this strange rash on your arms that just won't go away. Or raised red wheals have appeared on your chest and back. Or every time you eat shrimp, your lips and mouth swell, and you begin wheezing. All of these are symptoms of allergies and the form of allergy responsible for the greatest misery in the most people is allergic rhinitis, or hay fever.

Allergic rhinitis usually shows up before age 20, but it can develop at any age. In fact, it may be diagnosed as early as the first year of life. Today we know that allergic rhinitis is associated with several other respiratory illnesses, including asthma, and that it can significantly affect your ability to work or study.

The allergy ripple effect

The primary symptom of allergic rhinitis is a stuffed and/or runny nose. When your nose behaves like this, doctors say it's chronically inflamed. This constant inflammation provides the perfect breeding ground for viruses and bacteria, which can lead to numerous other problems, such as ear infections, sinus infections (sinusitis), and asthma. In fact, if you are prone to sinus infections, ask your doctor to check you for allergies.

Sinusitis is defined as an inflammation of the lining of the nasal sinuses, the hollow cavities within the cheekbones around your eyes and behind your nose. It can make an allergy attack feel like the sniffles. If you have sinusitis, chances are you also have a pounding headache, pressure behind your eyes and cheeks, toothache, green or gray nasal drainage, and postnasal drip. You may also lose your sense of smell and taste and have bad breath, along with chronic congestion.

About half of all people with sinusitis have allergies, and the theory is that the allergies lead to the sinus infections. It works like this: Normally, mucus and liquids drain from the sinuses through tiny openings about the size of a tip of a pen. Swelling due to an allergy can block that drainage, resulting in a buildup of mucus and providing a lovely spot for bacteria or viruses to thrive.

If allergies aren't treated, they can also lead to nasal polyps (pale, round outgrowths of the nasal lining) or swollen nasal turbinates (protruding tissues that line the inside of your nose). Sometimes surgery is required to correct these problems. Untreated allergies can also cause dental and facial abnormalities, as described later, and can affect speech development in children.

In addition to the most common symptoms associated with allergic rhinitis--sneezing, runny nose, and watery eyes--it often disturbs sleep, so people spend their days in a fog of fatigue. If congestion blocks your ear canals, it can also interfere with hearing and affect learning and comprehension.

Allergies can also affect appearance. For instance,the dark under-eye circles called allergic shiners can make allergy sufferers look as if they've been pulling a string of all-nighters, although they're actually caused by swollen blood vessels under the eyes. Because many people with allergies breathe through their mouths, they're more likely to develop a high, arched palate (the roof of the mouth), an elevated upper lip, and an overbite, which may require orthodontic work. Then there's the nasal crease, a line across the lower part of the nose that forms from constantly rubbing it (known as the allergic salute). Finally, allergy sufferers may look as if they're constantly tired, in part, because of swollen adenoids, the lymph tissue that lines the back of the throat and extends behind your nose.

Other common symptoms are chronic coughing; wheezing or shortness of breath; conjunctivitis, or pinkeye (red, swollen eyes); sore throat; frequent nosebleeds; postnasal drip; bad breath; canker sores; an itchy palate; stomach problems, such as bloating, belching, and heartburn; and irritability and depression.Just lovely, isn't it?

Allergy or irritation?

Just because your nose is running and you're sneezing, that doesn't mean you have allergies. You could have a cold, sinusitis, or the plain-Jane form of rhinitis that's not associated with allergies. Rhinitis is just a term doctors use to describe the symptoms that result from nasal irritation, such as congestion or runniness. These symptoms can mimic allergic reactions but are not the result of the IgE immune response that occurs in allergies.

Rhinitis that lasts less than six weeks is called acute, while persistent symptoms are called chronic. There's also infectious rhinitis, caused by viruses or bacteria, as with a cold or sinusitis, and vasomotor rhinitis, a run-of-the-mill drippy nose.

It works like this: Your nose normally produces mucus, which traps substances such as dust, pollen, pollution, and germs. Mucus flows back from the front of your nose and drains down your throat. If there's too much mucus, it drains down the front of your nose, too, and you get a runny nose. The more irritation, the more mucus your body produces to collect and dispose of the irritants.

Numerous other things can also cause rhinitis, including temperature changes (think about how your nose runs when it's cold out), spicy food, some medications (including blood pressure drugs, birth control pills, and aspirin and other nonsteroidal anti-inflammatory drugs, such as ibuprofen and naproxen), cigarette smoke, perfume, alcoholic beverages such as beer and wine, cleaning solutions, and chlorine in swimming pools. You may even find yourself getting congested when you're sexually aroused.

Pinning the blame

You're pretty sure you're allergic to something. The question is, what? Well, the only sure way to find out is with a skin or blood test. Keep in mind that you can be allergic to several of these triggers at the same time and that one allergy may disappear while another comes to take its place.