Lawsone

Lawsone (2-hydroxy-1,4-naphthoquinone), also known as hennotannic acid, is a red-orange dye present in the leaves of the henna plant (Lawsonia inermis) as well as jewelweed (Impatiens balsamica).^[3] Humans have used henna extracts containing lawsone as hair and skin pigments for more than 5000 years. In an acidic solution, lawsone can react via Michael addition with the protein keratin in skin and hair, resulting in a strong permanent stain that lasts until the skin or hair is shed. Lawsone strongly absorbs UV light, and aqueous extracts can be effective, sunless tanning sunscreens. Chemically, lawsone is similar to juglone, which is found in walnuts.

References

1. ^ Merck Index, 12th Edition, 5406.
2. ^ MSDS at Physical & Theoretical Chemistry Laboratory, University of Oxford
3. ^ Dweek, A. C. (2002). "Natural ingredients for colouring and styling". Int. J. Cosmetic Sci. 24: 287-302.