An ointment made from indigo naturalis, a dark blue plant-based powder used in traditional Chinese medicine, appears effective in treating plaque-type psoriasis, according to a report in the November issue of Archives of Dermatology.

Psoriasis is a chronic skin disease for which no cure exists, only therapies that bring it into remission, according to background information in the article. "Traditional Chinese medicine is one of the most frequently chosen alternative therapies in China and Taiwan, and psoriasis has been treated for centuries with topical and oral herbal preparations," the authors write. "Indigo naturalis is one of the Chinese herbal remedies that has been reported to exhibit potential antipsoriatic efficacy. However, long-term systemic use has been occasionally associated with irritation of the gastrointestinal tract and adverse hepatic effects." Researchers conducted a randomized trial of an ointment containing indigo naturalis in 42 patients with treatment resistant psoriasis.

Participants enrolled in the study between May 2004 and April 2005 and applied the indigo naturalis ointment to a psoriatic plaque on one side of their body (usually on the arm, elbow, leg or knee) and then a non-medicated ointment to a parallel plaque on the other side of their body. The researchers assessed and photographed patients' skin plaques at the beginning of the study and again after two, four, six, eight, 10 and 12 weeks.

After 12 weeks of treatment, the plaques treated with indigo naturalis ointment showed significant improvement in scaling, erythema (redness) and induration (hardening) when compared with the plaques treated with non-medicated ointment. "Weighting the sum of scaling, erythema and induration scores by the lesion area and comparing between the start and end of the study, the indigo naturalis ointment–treated lesions showed an 81 percent improvement, whereas the vehicle [non-medicated] ointment–treated lesions showed a 26 percent improvement," the authors write.

Of the 34 patients who completed the study, none experienced worsening psoriasis in the areas treated with indigo naturalis, while the treated plaques were completely or nearly completely cleared for 25 of them (74 percent). None experienced serious adverse effects. Four patients reported itching after applying the indigo naturalis ointment, but only for a couple of days at the start of treatment.

"In conclusion, we present a randomized controlled trial showing the use of topical indigo naturalis ointment for the treatment of chronic plaque psoriasis to be both safe and effective," the authors write. "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."