Indigo

Indigo (from the Greek indikon = Indian) is a natural blue dye obtained from the indigo plant (Indigofera tinctoria), and in the past in Germany from woad (Isatis tinctoria) or 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 to color textiles (especially uniforms).

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

Studies show good healing of mild to moderate psoriasis through the local application of indigo naturalis in Lindioil ointment. The most effective concentration was 200 μg/g ointment. Participants achieved 75% and 90% reduction in PASI scores (PASI 75 and PASI 90 respectively) from baseline to week 8 with no serious side effects 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