I'd like to know what causes postnasal drip and how a person get relief from this condition.

A. Postnasal drip is mucus from the nose or sinuses that, if not blown into a handkerchief, drips down the back of the throat. Many people are bothered by it while lying in bed at night. There is usually inflammation of the nose (rhinitis, from the Greek word for nose) or sinuses (sinusitis).

There are four main types of rhinitis, each with different treatments.

People with allergic rhinitis have noses that react to various substances by releasing a chemical called histamine. Histamine makes the inside lining of the nose swell, become congested and produce mucus. Triggering substances include pollens, molds, animal dander, house dust and occasionally foods. Treatment begins with avoiding exposure to provoking substances, and using over-the-counter antihistamine medications, such as Chlor-Trimeton or Dimetane. Because antihistamines tend to make you drowsy, many people take decongestants as well, which tend to be stimulating. For more troublesome problems with postnasal drip from allergies, you can use prescription nose sprays such as beclomethasone, a steroid, or cromolyn, which blocks the release of histamine. Or you can take allergy shots.

Nose and sinus infections also cause postnasal drip and range from acute, short-lived problems such as the common cold, to long-standing ones, such as chronic sinusitis. For the common cold, over-the-counter cold remedies containing antihistamines and decongestants help ease nasal stuffiness. Decongestant nose sprays also help, but you shouldn't use them for more than three days to avoid "rebound" congestion. For a sinus infection, often caused by bacteria, antibiotics are in order.

Another common cause of postnasal drip, vasomotor rhinitis, is not well understood. Vasomotor refers to changes in the blood vessels lining the inside of the nose. Certain things make these vessels swell, leading to congestion, stuffiness and postnasal drip. Among the varied triggers of vasomotor rhinitis are stress, changes in emotion, smoking, drinking alcohol, underactive thyroid gland, pregnancy, certain high blood pressure drugs such as reserpine, and changes in temperature and humidity. Treating vasomotor rhinitis can be difficult, but you can try avoiding any triggering factors, use saline (salt water) nose sprays, such as NaSal, take decongestant pills and exercise regularly. Sometimes beclomethasone nasal spray helps this condition.

The fourth main cause is something physically blocking the nasal passages. Nasal polyps and a deviated or crooked nasal septum are common culprits. Polyps are small, fleshy, grape-like growths inside the nose. The nasal septum is the thin vertical partition separating the right from left nasal passages. If these conditions are severe, you need surgery to correct them. Q. At what point does rectal bleeding become a serious cause for concern? I've been diagnosed as having hemorrhoids and try to watch my diet, but still occasionally have a bloody stool. This does not always coincide with a difficult bowel movement. Sometimes it's completely unexpected. I'm 35 and in good general health, but there is a history of cancer, including colon cancer, in my family. A. Cancer of the rectum and colon is the number two cancer killer, so it's worth paying attention to the warning signs of this disease. Along with rectal bleeding, a change in bowel habits is another clue to a potentially serious intestinal problem.

Having said that, you should know that most rectal bleeding is not cancer. Many people occasionally have bleeding with bowel movements, especially large ones or those that follow a lot of straining. Hemorrhoids -- swollen veins around the anal opening -- are the most common cause. An anal fissure -- a small tear in the anal opening -- can also cause blood in the stools and a sharp tearing pain with bowel movements.

To tell where the bleeding is coming from, your doctor will usually look at the anus, rectum and last part of the colon through a narrow tube called a sigmoidoscope that's inserted into the rectum. To make sure that the bleeding isn't coming from somewhere farther inside the intestines, your doctor may order a barium enema -- an X-ray examination of the colon -- or in some cases colonoscopy. In this procedure, a doctor passes a longer tube through the entire four to six feet of your colon and checks for polyps, cancers or sites of bleeding.

Once your doctor is convinced that the bleeding is from your hemorrhoids, you can rest easy about something else being wrong. If the bleeding is bothersome enough, you can have hemorrhoid surgery. But be sure to keep your doctor informed about any changes, new symptoms or if the bleeding persists. Occasionally, you will need to have some of these test repeated.

In any event, I recommend following the American Cancer Society guidelines for cancer screening. For rectal and colon cancer, all adults 40 and older should have a yearly check of their stool for trace amounts of blood. After age 50, they should have sigmoidoscopy exams every three to five years after two normal exams one year apart.

Of course, your doctor may modify these guidelines to fit your particular situation. For instance, people with a strong family history of colon cancer, as you may have, should have screening examinations earlier in life and in some cases more frequently.