Q: I can't urinate in a public restroom. I've heard of a condition called "bashful" or "shy" bladder. What is that and can it be treated?

A: A "shy" or "bashful" bladder -- known in medical jargon as paruresis -- is a real syndrome. People with this problem can't urinate in public bathrooms.

The problem is common. About 20 million Americans have it to some degree. About 90 percent are men.

No one knows the cause. The simplest explanation is that it's a physical reaction to anxiety. Anxiety can cause heart palpitations or shakiness. It can also cause smooth muscles in the urinary tract to clamp down.

You would probably know if you had social anxiety disorder. In this disorder, you wouldn't just have anxiety in bathrooms. You would experience anxiety in many different social situations.

If the problem just started, see your primary care doctor for a general checkup. You'll want to know if there's a health reason for it. For example, if there's a problem with your bladder, prostate, or kidneys.

Assuming you're otherwise healthy, then match your approach to the situation. For the simplest forms of shy bladder that happen in specific situations, it may be enough to understand where you have trouble and avoid those places.

Cutting down on alcohol may also help. Alcohol causes a greater urge to urinate while possibly swelling the prostate. That, in turn, makes it harder to start your stream.

If you have a problem that keeps you from a meaningful social life or blocks your progress at work, speak with a mental health professional.

Anti-anxiety drugs don't always relieve shy bladder. But relaxation and behavior therapy techniques can work. You may also want to learn whether the problem is related to performance anxiety, or whether you're physically self-conscious.

(Michael Craig Miller, M.D., is a Senior Medical Editor at Harvard Health Publications. He is an Assistant Professor of Psychiatry at Harvard Medical School and an associate physician at Beth Israel Deaconess Medical Center, Boston, Mass.)

(For additional consumer health information, please visit http://www.health.harvard.edu.)