Q. What is haole rot?

A. Tinea versicolor — sometimes called haole rot locally — appears as spots on the torso, back and face that may be darker than the rest of the skin in those with light skin or lighter in those with dark skin. The patches usually have a fine scale and often combine to form larger patches of various colors (hence its real name) — white, tan, brown, and occasionally reddish or pinkish.

It's a common, harmless skin infection caused by a yeast called Malassezia furfur, but is neither contagious nor due to poor hygiene. Nearly everyone has naturally occurring malas-sezia on their skin, but when it changes from the dormant yeast form to the more active mycelial form, then spots can appear. Tanning makes the spots more noticeable.

Most common in teens and young adults, the sometimes-itchy spots come and go, usually disappearing without treatment in old age. Malassezia infection also causes dandruff and a common rash called seborrheic dermatitis, which affects the scalp, face and chest.

Nonprescription treatments include 1 percent selenium sulfide (Selsun) shampoo applied to the skin from neck to waist for 30 minutes daily for a week (I'd also shampoo the scalp the first few days) and clotrimazole (Lotrimin) cream twice a day for 3 weeks, or Lamisil cream once a day for a week.

Prescription treatments include ketoconazole 2 percent shampoo applied to damp skin in a thin layer and left on for five minutes for three straight days, or Selsun 2.5 percent lotion applied daily for 1 week — allow to dry for 10 minutes before showering. Alternatively, leave Selsun on your body for 12 to 24 hours, rinse it off, and repeat weekly for four weeks.

Be patient — it may take months for the spots to go away, but you'll notice that no new spots appear.

Haole rot often comes back. To prevent this, repeat the above treatments the first and second day of each month, or use over-the-counter ketoconazole (Nizoral) shampoo lathered on the chest and back once a week and left on for five minutes before showering.

Ketoconazole 400 mg as a single oral dose results in short-term cure in 90 percent of cases, but don't shower for eight to 12 hours afterward, because it is delivered by sweat to the skin. But a single dose may not work in hot, humid areas, and more doses increase the risk of hepatitis for a completely benign disease. Furthermore, without preventive therapy, tinea versicolor will reoccur more than 80 percent of the time over the next two years. So go with the safer creams or shampoos if at all possible.

Dr. Landis Lum is a family-practice physician for Kaiser Permanente and an associate clinical professor at the University of Hawai'i John A. Burns School of Medicine. Send questions to Prescriptions, Island Life, The Advertiser, P.O. Box 3110, Honolulu, HI 96802; fax 535-8170; or to islandlife@honoluluadvertiser.com. This column is not intended to provide medical advice.