November 18 (HealthDay News) -- Indigo ointment may benefit patients with plaque-type psoriasis, Taiwanese researchers say.

They studied 42 people with treatment-resistant psoriasis who were treated with an ointment made from indigo naturalis, a dark blue, plant-based powder used in traditional Chinese medicine. The patients applied the ointment to a psoriatic plaque on one side of their body (usually the arm, elbow, leg or knee) and applied a non-medicated ointment to a psoriatic plaque on the other side of their body.

The patients' skin plaques were assessed at the start of the study and again after two, four, six, eight, 10 and 12 weeks. After 12 weeks, the plaques treated with the indigo ointment showed an 81 percent improvement in scaling, redness, and hardening, compared to a 26 percent improvement in the plaques treated with the non-medicated ointment.

None of the 34 patients who completed the study experienced worsening psoriasis in the areas treated with the indigo ointment, and the treated plaques were completely or almost completely cleared in 25 (74 percent) of those patients. Four patients experienced itching after applying the indigo ointment but only for a few days at the start of the treatment. There were no serious side effects, the researchers said.

The study, published in the November issue of the journal Archives of Dermatology, shows the indigo ointment is safe and effective, Dr. Yin-Ku Lin, of the Chang Gung Memorial Hospital and Chang Gung University in Taoyuan, and colleagues, said in a news release issued by the journal.

"Future research for a more potent extraction from this crude herb that can provide better absorption and convenience would help improve patient compliance with the treatment regimen. However, much more research will be necessary to clarify the pharmacology of indigo naturalis," they concluded.

SOURCE: JAMA/Archives journals, news release, Nov. 17, 2008