Q. Several weeks ago I started to break out in a skin rash across my back. Over time, the rash grew worse. It was slightly itchy, but otherwise more a worry than a nuisance.

My doctor said I had something called pityriasis rosea, and that it would take time to clear. I hadn't heard of this condition before. What can you tell me about it?

A. Pityriasis rosea is a skin rash that usually affects adolescents and young adults. It typically occurs in the spring and fall, and is probably caused by a virus, though it is not contagious.

Pityriasis comes from a Greek word meaning bran. The condition is so named because its slightly scaly rash was thought to resemble fine husks of grain. Rosea refers to its rosy pink, salmon or light brown color.

The condition usually emerges as a single large oval spot on the skin measuring up to several inches across. It's followed by many small oval spots that are slightly raised and scaly. The initial spot is called the "herald patch," because it signals the development of the rash that typically follows.

The rash tends to occur on the back and chest, and sometimes on the upper arms and legs. It usually doesn't spread to the face, hands or feet. A telltale feature of pityriasis rosea is that the rash aligns itself with the natural lines of the skin. Across the back, it appears to follow the ribs as they slant down and out on both sides, giving it the shape of a Christmas tree.

At times, the rash may be itchy, but it may cause no symptoms at all. There's no cure, and the rash usually clears within eight weeks. In rare cases, it can last many months before clearing.

Some medicines can trigger a rash resembling pityriasis rosea. These include captopril, clonidine, metronidazole and barbiturates. Syphilis also can cause a rash that is similar.

There's no specific test for pityriasis rosea; doctors diagnose it by appearance. Although treatment is generally not necessary, steroid pills or creams may be prescribed if your rash causes a lot of itching. Antihistamine pills may also help the itching. The medications will not make the rash clear faster.

Sunlight seems to help the rash in some people. For this reason, doctors have also tried ultraviolet light therapy for pityriasis rosea. This isn't generally needed, but it does help some people with severe cases.

Treating Motion Sickness

Q. I get motion sickness easily. I've tried several remedies without success. What else can I do?

A. Motion sickness can be tricky to prevent or treat. First, make sure you've tried a variety of different medicines. If one doesn't work, try another. Many are available without a prescription.

* Antihistamines are the medicines most often used to prevent motion sickness. They settle the balance system in your inner ear, and also make you drowsy. These include cyclizine (Marezine), dimenhydrinate (Dramamine), diphenhydramine (Benadryl), and meclizine (Bonine).

* Anti-cholinergics work in a similar way. Scopolamine comes in a prescription pill (Scopace) or a patch (Transderm-Scop) that you wear behind your ear. Besides drowsiness, it can give you dry mouth and slightly blurred vision.

* Phenothiazines block the vomiting center in the brain. Promethazine (Phenergan) is a prescription medicine in this group.

If these medicines don't work, there are a few other things your doctor can try. One is using a tranquilizer such as Valium or Ativan. Another is using a low dose of a stimulant medicine along with a motion sickness pill or patch.

Research in military recruits has shown that small doses of a stimulant such as Dexedrine or Ritalin, when added to scopolamine, reduces severe motion sickness. However, stimulants have a high potential for abuse, and they are not approved by the FDA for treating motion sickness.

Finally, because motion sickness is somewhat of a state of mind, hypnosis might help if all else fails.Jay Siwek, chairman of the department of family medicine at Georgetown University Medical Center, practices at the Fort Lincoln Family Medicine Center and Providence Hospital in Northeast Washington.

Consultation is a health education column and is not a substitute for medical advice from your physician. Send questions to Consultation, Health Section, The Washington Post, 1150 15th St. NW, Washington, DC 20071. Questions cannot be answered personally.