Many travel books recommend Lomotil for traveler's diarrhea. My doctor tells me not to use it. Who's right?

Lomotil (diphenoxylate) slows down intestinal mobility and therefore reduces trips to the bathroom. It is very useful for days that you travel or go sightseeing. However, it does not cure travelers' diarrhea. Generally, travelers' diarrhea is a self-limited condition that lasts only a day or two whether you take medication or not. Drink clear fluids and juice, eat bland foods or nothing at all.

Do not take Lomotil if you have fever, blood in the stool, feel unusually sick or the diarrhea lasts more than three days. You may have a more serious infection. By slowing intestinal mobility, Lomotil gives the causative organism a better chance to invade the lining of the intestine and prolong the duration of illness.

Are the detectors that you have to walk through at airports safe when you are pregnant?

The detectors at domestic airports and at most airports around the world are metal detectors. These emit no radiation and are therefore safe, but some detectors overseas do apparently use radiation.

No matter where you are, if you tell the security attendants you are pregnant they will check you with a hand-held detector.

Do you need anti-malaria pills for visiting China?

The World Health Organization reports that malaria does exist in China, mostly in southern China. However, these cases are in remote, rural areas far from the usual tourist routes. No traveler is known to have contracted malaria in China in recent years. For ordinary travel in the country, no health authority currently recommends malaria prophylaxis.

I am going on a cruise in spite of the fact that I get seasick. Do the patches you paste behind your ears really work?

You are referring to Transderm-Scop patches, which have scopolamine as the active ingredient. These do work, but there are side reactions: a dry mouth and, sometimes, dizziness. These patches are available only by prescription. Most ship's physicians stock them.

In fact, seasickness is rare on cruises. Cruise lines choose itineraries to avoid rough seas, ships have stabilizers, and sophisticated weather forecasting helps captains to navigate around storms. Obviously, seasickness is not good for repeat business.

Is it true that getting a tan at a tanning parlor protects against sunburn when you go to the tropics?

Yes, but the benefits do not outweigh the disadvantages.

It is true that any tan will protect you from subsequent sunburn. It is also true that tanning machines emit UVA radiation, the "tanning" rays of the sun, but not the UVB radiation, the "burning" rays.

The problems: There is growing evidence that UVA too may be harmful for your skin, although at a slower rate than UVB. Also, while a tan may prevent burning, it does not prevent long-term skin damage. Long-term damage, whether from UVA or UVB and whether you are tanned or not, is cumulative over a lifetime. Therefore, an artificial tan just adds to the long-term damage.

Dr. Karl Neumann is a pediatrician in Forest Hills, N.Y., who writes about travel and health.