Almost everyone knows what it feels like to have a runny, stuffed-up nose at times. Often these symptoms are accompanied by a headache in the area around the eyes, nose and temples. People with allergies are especially prone to these symptoms. They are signs of rhinitis and sinusitis, two very common medical problems. It is estimated that up to 40 million American adults and children have one or both of these conditions.

Although not life-threatening, rhinitis and sinusitis can make you miserable. At their worst, they can keep you from functioning normally, and may lead to life-threatening complications. Fortunately, there are things you can do to prevent these problems. And effective treatments exist when these symptoms do arise. If you have allergies, you are more likely to develop rhinitis or sinusitis than are persons without allergies. This makes it even more important to keep your allergies under control and to prevent rhinitis and sinusitis from occurring.

The word rhinitis means simply "inflammation of the nose." The nose normally produces a fluid called mucus. This fluid is normally thin and clear. It helps to keep dust, debris and allergens out of the lungs. Mucus traps particles like dust and pollen as well as bacteria and viruses.

Normally, mucus drains down the back of the throat, but you're not aware of it due to its relatively small amount and thin consistency. But when the nose becomes irritated, it may produce more mucus, which becomes thick and pale yellow. The mucus may begin to flow from the front of the nose as well as the back. Substances in the mucus may irritate the back of the throat and cause coughing. This increased mucus draining down the throat is called postnasal drip.

Rhinitis may be caused by irritants or allergens (substances that provoke an allergic response). In response to these substances, the cells of the body release histamine and other chemical mediators. These are the substances that cause the symptoms of allergic rhinitis-sneezing, runny nose, and itching, watery eyes.

In many people, rhinitis is a temporary condition that clears up on its own after a few days. In others, especially those with allergies, rhinitis is a chronic problem-one that is nearly always present or that recurs often. Rhinitis is often classified into several types:

Allergic rhinitis. Rhinitis caused by an allergic reaction may be either seasonal-occurring only at certain times of the year-or perennial-occurring year round. Seasonal allergic rhinitis is sometimes called "hay fever." It is an allergic reaction to pollen from trees and grasses. Ragweed pollen is another frequent culprit causing hay fever. This type of rhinitis occurs mainly in the spring and fall, when these pollens from trees, grasses and weeds are in the air.

Perennial allergic rhinitis is caused by allergies to substances that are present year round. The chief causes of this type of rhinitis are allergies to dust mites, mold, animal dander and cockroach debris.

Nonallergic rhinitis. Sometimes perennial rhinitis is not caused by allergic triggers. It may be caused by overuse of topical nose sprays, hormonal changes, structural abnormalities of the nose (such as septal deviation), and occasionally by medications. Often, the cause of this type of rhinitis is not well understood, but it is commonly present in patients with asthma. Its symptoms are similar to those produced by allergy.

Infectious rhinitis. Perhaps the most common form of rhinitis, infectious rhinitis is also known as the common cold. It is caused by infection with a cold virus that takes up residence in the mucous membranes of the nose and sinus cavities.

It can be hard to tell the difference between allergies and the common cold. There are more than a hundred strains of cold viruses. Each tends to become widespread at certain times of the year, which is why you may mistake a cold for a seasonal allergy.

Most cases of rhinitis go away once the source of irritation is gone. In the meantime, decongestants can help to relieve a stuffy nose. Be very careful, however, with the use of over-the-counter decongestant nasal sprays. Overuse of these products can actually make your stuffy nose worse. If used chronically and then stopped, after the effects of these products wear off, the tissue inside the nose and sinuses tends to become swollen. This can prompt you to use more of the medication, after which these tissues swell even more. A vicious cycle can begin if you keep using the product. As your body adjusts to the chronic medication, you need more of the medication more often to relieve the side effects. At first you may get relief, but in the long run the symptoms are worse. You then try to relieve the symptoms with more medication, which in turn worsens the side effects, and so on. All the while the underlying cause of your stuffy nose is not being treated.

Perhaps the most widely used type of medication used to control the symptoms of rhinitis are the antihistamines. These medications counteract the affects of histamine, the naturally occurring chemical that causes allergy symptoms. The chief side effect of antihistamines is drowsiness. A number of new antihistamines have been developed that do not cause drowsiness in most people. These medications are available with a doctor's prescription. Cromolyn nose spray, available over the counter, may be helpful for allergic rhinitis and causes essentially no side effects. The most effective medications for allergic rhinitis are the prescription corticosteroid nose sprays that reduce allergic inflammation, usually without causing systemic side effects.

Sinusitis is an infection or inflammation of the sinuses. A sinus is simply a hollow space. There are many sinuses in the body, including four pairs inside the skull. These are called the paranasal sinuses. They serve to lighten the skull and give resonance to the voice.

The paranasal sinuses are lined with the same kind of tissue that lines the inside of the nose. The same things that can cause swelling in the nose-such as allergies or infection-can also affect the sinuses. When the tissue inside the sinuses becomes inflamed, mucus discharge is increased. Over time, air trapped inside the swollen sinuses can create painful pressure inside the head. This is what is known as a "sinus headache."

The best course for preventing rhinitis and sinusitis is to keep your nasal passages as free and clear as possible. This is particularly important if you have allergies.

If you have chronic rhinitis and tend to get repeated bouts of sinusitis, your doctor may prescribe a steroid nasal spray. Taken every day, this medication will help to keep the nasal and sinus passages from becoming inflamed. (For more details on sinusitis, see the Asthma and Allergy Answer article on, "What is Sinusitis?")

To the extent possible, avoid exposure to the things that trigger your allergies. Keep cigarette smoke out of your home and avoid it in other places as much as possible.

Most important, keep your doctor informed of your symptoms. Together you can devise a plan of action to take before a minor case of rhinitis or sinusitis turns into a bigger health problem.