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IUPAC name 2-Hydroxy-1,4-naphthoquinone
Other names Hennotannic acid
Natural Orange 6
C.I. 75480
CAS number 83-72-7
PubChem 6755
Molecular formula C10H6O3
Molar mass 174.15
Appearance Yellow prisms
Melting point

195-196 °C (decomposition)

R-phrases R36 R37 R38
S-phrases S26 S36 S37 S39
LD50 100 mg/kg
Related Compounds
Related naphthoquinones Juglone
Except where noted otherwise, data are given for
materials in their standard state
(at 25 °C, 100 kPa)

Infobox disclaimer and references

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.


  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.
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Lawsone". A list of authors is available in Wikipedia.
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