The chemistry of heena (Mehndi)

Heena (Mehndi) is a green natural dye prepared from the plant Lawsonia inermis, that is used to decorate parts of the body and dye the hair a dark red color for a short amount of time.This dye is completely natural and has no side effects.

The naturally occurring chemical constituents of heena powder are generally referred as ' Biochemicals' or 'Phytochemicals', because they occur naturally within plant matter.

The main phytochemicals in heena leaves are :

• Sugar
• Lawsone
• Tannin
• Gallic acid
• Fraxetin
• Resin
• Coumarins

These are mainly responsible for the colourant property of the heena leaves.

Enriching your heena paste by extra tannin which is widely found in tea or adding extra gallic acid which is widely found in cloves will usually help to deepen the colour of your heena stain. You can also add curd in heena paste to enrich and nourish your hair .

LAWSONE MOLECULE :

A small red-orange dye molecule present in the leaves of the henna plant.

• The molecule of lawsone is 2-hydroxy-1, 4-naphtoquinone. It contains 10 carbons, 6 hydrogens, and 3 oxygens.

Lawsone has an affinity to the protein, keratin, which is present in hair and skin. Thus, it is able to react with the protein, keratin, and stain the skin or hair.

Staining the Skin :

• Chemically, the henna leaves contain a red orange pigment, lawsone, or hennotannic acid that is released when the henna leaves are crushed in an acidic solution.

• The lawsone dye molecule is small enough to penetrate through the stratum corneum which is the outermost layer of the skin. The lawsone molecule goes straight down the stratum cornuem and does not blot allowing to keep the design clear on the skin.

 If you put henna paste on skin or hair, the lawsone molecules will migrate from the plant pulp, into keratin, leaving a red-orange stain. 
This action is similar to putting a wet teabag on a white cloth.  The longer you leave the wet teabag on the cloth, the darker the stain.  
Similarly the longer you leave the henna paste on skin or hair, the more lawsone molecules will have the opportunity to migrate into the keratin,though five to six hours generally is enough for maximum absorption of henna.  
As more lawsone molecules migrate into keratin, the more saturated and rich the color.

 The other Phytochemicals in heena leaves are :

• 1,2-Dihydroxy-4-Glucosylnaphthalene
• 1,3-Dihydroxynaphthalene
• 1,4-Diglucosyloxy-2-Hydroxynaphthalene
• 1,4-Naphthaquinone
• 1,4-Naphthkquinone
• 4-Glucosyloxy-1,2-Dihydroxynaphthalene
• Aesculetin
• Cosmosiin
• Beta-Sitosterol
• Cynaoside
• Daucosterol
• Esculetin
• Glucose

and many more but I have given some of them.

 The naphthoquinones in henna have received the greatest research attention, as the dye properties, antimicrobial, and strong antioxidant effects proceed from these.  
Henna contains a number of naphthoquinones including 2-methoxy-3-methyl- 1,4-naphthoquinone and lawsone (2-hydroxy-1,4-naphthoquinone). 
These henna naphthoquinones are derived from naphthalenes. A small number of naphthalenes, lawsoniaside (1,2,4-trihydroxynaphthalene-1,4-di-β-D-glucopyranoside) 1,2,4-trihydroxynaphthalene-1-O-β-D-glucopyranoside three methyl naphthalene carboxylates, lawsonaphthoate A-C, and 1,2-dihydroxy-4-Oglucosyloxynaphthalenehave been isolated from henna stems and leaves.

AVOID BLACK MEHENDI :

Natural mehendi, when applied to the skin rarely causes any adverse reactions. There is no such thing as black mehendi. In order for mehendi to produce a black colour chemicals that are unsafe for your skin have been added. Black mehendi should be avoided. A chemical dye known as p-Phenylenediamine (PPD), which is not authorized for use on the skin by the FDA is often added to the natural mehendi to produce a black colour.

Thank you :) 😊