Indigo

Indigo (from Greek indikon = the Indian) is a natural blue dye obtained from the indigo plant (Indigofera tinctoria) and, in former times in Germany, from the woad (Isatis tinctoria) or also Baphicacanthus cusia. Indigo was already used in Egypt 4000 years ago.

In the Middle Ages, indigo was the only available blue dye that could be used for dyeing textiles (especially uniforms).

The plants themselves do not contain indigo, but the glycoside of indoxyl, indican, which must be converted into indoxyl by hydrolysis. Subsequent oxidation in air produces blue indigo from the yellow indoxyl. To obtain the dye, the plants were subjected to a fermentation process.

Studies show good healing of mild to moderate psoriasis by local application of indigo naturalis in Lindioil ointment. The most effective concentration was 200 μg/g ointment. Participants achieved 75% and 90% reductions in PASI scores (PASI 75 and PASI 90, respectively) from baseline to week 8 without serious adverse events within the 20-week observation period.

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3. Lin YK et al. (2018) Comparison of indirubin concentrations in indigo naturalis ointment for psoriasis treatment: a randomized, double-blind, dose-controlled trial. Br J Dermatol. 178:124-131
4. Hoffmann J et al. (2020) New Herbal Biomedicines for the Topical Treatment of Dermatological Disorders. Biomedicines. 8(2):27 https://www.mdpi.com/2227-9059/8/2/27