Henna (Lawsonia inermis)
Also known as: Mehndi; mehendi; red henna; lawsone (its colouring compound)
INCI name: Lawsonia Inermis (labels may add 'leaf powder' or 'leaf extract')
What it does
Powdered dried leaves of the henna shrub. Its colouring compound, lawsone, stains hair and skin orange-red to red-brown; dried leaves contain about 1–2% lawsone.
Benefits
Pure henna is one of the least allergenic ways to colour hair; true allergy is rare. The EU's scientific committee judged henna safe as a hair dye when prepared as 100 g of powder to 300 ml of water, based on henna containing up to 1.4% lawsone.
Concerns & Risks
The main danger is adulteration. Testing of products sold as henna has repeatedly found undeclared PPD: in all 10 henna-based hair colours in one Brazilian study, in 2 of 11 commercial preparations in a Spanish one, and in up to 36% of samples in a Polish one. Pure henna cannot turn hair black; a 'henna' that gives black is either blended with indigo or has PPD in it. True allergy, though rare, has been reported, including hives, asthma and a streaming nose and eyes in people who handle it at work. Put on the skin of babies with G6PD deficiency, henna has caused dangerous breakdown of red blood cells. It can still irritate a sensitive scalp.
Comedogenic rating
Non-comedogenic (0)
Suitable for
Most people, including many who cannot use PPD dyes, provided it is pure henna with a full ingredient list, and still after a skin test
Avoid if
On babies or young children, especially with known or suspected G6PD deficiency; you have a known henna allergy; the product is 'black henna' or lists PPD, toluene-2,5-diamine or other synthetic dyes
Typical concentration
SCCS-assessed use: 100 g powder in 300 ml water, henna with up to 1.4% lawsone. Henna is not among the restricted hair-dye substances in EU Annex III. US: an approved colour additive for hair, not for staining skin. India: henna powder must meet BIS IS 11142 (Cosmetics Rules 2020, Ninth Schedule); we could not see that standard's content.