henna-ed hair, a photo by gumonyershoe on Flickr.

Dear Nicki,

I’ve been using henna as a natural alternative to hair dye. it makes my hair all one color but I think it is safer than regular hair dye. Any thoughts?

-Dyeing Doll

Dear Dyeing,

Henna, also known as Lawsonia inermis or the mignonette tree, is a flowering plant used to dye skin, hair, fingernails, leather, and wool. It is rumored beautiful and substantial women, from Nefertiti to Lucille Ball, used it to achieve their desired hair color (Encyclopedia of Hair, 2006).

Natural henna, the specific type of henna used to dye hair, is derived from the dried leaves of the Henna plant. Dried leaves are crushed and made into a paste, which traditionally was mixed with water and agents such as indigo or chamomile as conditioning agents before being applied to the hair. Keep in mind that other types of non-”natural” henna, including neutral henna and black henna, will not affect your hair color.

Unfortunately, natural henna is terrible for your hair. The three big reasons:

#1. Henna makes it impossible to condition your hair.

The active ingredient in henna, is lawsone, also known as 2-hydroxy-1,4-naphthaquinone. Lawsone, also present in walnuts, works best at acidic (low) pH and when applied with heat. Unfortunately, over time, lawsone builds up on the hair, making it difficult, if not impossible, for conditioning agents to penetrate the hair (Chemistry and Technology of the Cosmetics and Toiletries Industry, 1996). As beauty expert Eva Scrivo notes, “[With henna use] treatments, conditioners, and even natural oils from the hair are not able to get through that heavy layer of gunk covering the cuticle.”

#2. Henna eventually leads to hair breakage.

Henna is one of those agents that will harm your hair. There are several reasons for this. One, the lawsone in henna reacts with the hair in a largely unknown mechanism that results in toxic products being built up on the hair (Chemistry and Technology of the Cosmetics and Toiletries Industry, 1996). These toxic products can cause oxidative damage to the hair if they are not properly removed. Two, as previously mentioned, henna prevents the penetration of conditioning agents into the hair cuticle, rendering your treatments futile. Lastly, henna dehydrates the hair, making it more susceptible to long-term damage (Eva Scrivo on Beauty, 2009).

#3. Henna may harm your health or your skin.

Wait, I know long-term readers are thinking, did she just say something could be harmful? Despite the popular, very cautious, natural approach towards beauty products that has taken place lately, I am reluctant to declare anything is “unsafe” unless it has been proven so in strong, logical studies. That having been said, although the lawsome in henna has been proven not to be genotoxic (Mutation Research/Genetic Toxicology and Environmental Mutagenesis, 2003), it has been shown to cause a life-threatening hemolysis in patients with a condition known as glucose-6-dehydrogenase deficiency (G6PDH) (Archives of Disease in Childhood, 2001).

Now don’t be alarmed and think you need to run out for a G6PDH blood screen if you’ve used henna recently – G6PDH typically presents in childhood with symptoms like jaundice and anemia. Affected patients are usually males (due to X-linked inheritance) in Africa, the Middle East, or South Africa (presumably because the disease protects against malaria).

That having been said, for men/women in the U.S. and Europe (my current popular demographic, thank you very much, Alexa stats), henna has been shown to frequently cause sensitization of the skin and a resultant contact dermatitis (rash) (Textbook of Cosmetic Dermatology, 2004).