How Henna Colors Hair

By Joe Parker of Cush Cosmetics

The Origins of Henna

Before I delve into mechanics of henna, I think it’s important to know a little bit about its rich history.  The henna bush is indigenous to North Africa, the Middle East, south Asia, and northern Australia.  As far back as the times of ancient Egypt, people have used henna to dye hair, skin and fingernails.  They would harvest the henna leaves at the end of the summer season just before the rainy season began because the leaves had the highest amount of dye content during that time period.  The leaves would be dried, milled, and sifted; and then later sold as a fine powder for dying.

What is Henna Exactly?

The active ingredient that enables henna to color hair is lawsone- which is also known as 2-Hydroxy-1,4 Napthaquinone.   Lawsone is a weak organic acid that has a typical concentration of 1.3-1.5% in henna leaves that are harvested at the height of the summer season, as mentioned above.  In order for lawsone to be effective, it must be preserved.

How is Lawsone Preserved During the Manufacturing Process?

Lawsone is unique because of its structure.  It’s an extremely unstable negatively charged structure due to the presence of 2 carboxyl groups (C=O) and one acid group (OH).   It will ionize and then react (decompose) quickly, which makes it ineffective for hair coloring; therefore it needs to be preserved.  In today’s manufacturing practices, lawsone is preserved with citric acid during the milling process. However, during ancient times, lemon juice or tea was added to the henna powder to create an acidic paste of permanent hair colorant.  The over abundance of protons from the citric acid make it less likely that the acid group or carboxyl groups on the lawsone molecule will ionize and decompose.  Remember, it’s the release of lawsone in the henna leaves that gives henna its pigment.

Tip:  Make sure the Henna product you purchase has citric acid on the INCI ingredients listing.  If the lawsone has decomposed, it will not color the hair.

The Color of Henna

Lawsone’s color is red to orange only.  So when you see henna in colors other than reddish orange, other pigments have been added.  The important question to ask is, “What are those pigments?”  Are they natural pigments such as indigo, turmeric, catechu, amal, vashma or black walnut shells?  If so, you should have a basically safe colorant for your hair.  However, if you see colors listed like the ones below, the odds are that the manufacturer has added a synthetic dye, which studies suggest are toxic.

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