A topical preparation containing Indigo naturalis powder has been shown in a randomized trial to be effective in treating plaque-type psoriasis, also called Psoriasis Vulgaris, the most common type of this chronic skin disease.
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.”
Researchers suggest further research into the pharmacology of indigo naturalis to be able to come up with more potent and better absorbed formulations. Source