Henna (Lawsonia inermis) is a plant native to Africa which produces a red-orange dye molecule, called lawsone. This molecule has an affinity for bonding with protein, and thus has been used to dye skin, hair, and fingernails and has been used for body art (temporary tattoos) and hair dye since the Bronze Age (see the photo on the right). The United States Food and Drug Administration has not approved henna for direct application to the skin but only to hair as a dye.
The Henna dye can be brown, red or green and produces temporary tattoos that are usually harmless and wear off in a matter of days. To produce a darker color, some tattoo artists add a chemical called paraphenylenediamine. Thus, the fast black stains of “black henna” are not made with henna, but are from paraphenylenediamine (PPD). This can cause severe allergic reactions and permanent scarring.
The New England Journal of Medicine published a case report of Allergic Contact Dermatitis from a Henna Tattoo showing the blistered hands of a 19-year-old Kuwaiti woman who had a temporary tattoo applied at a wedding 8 days earlier. She was treated with topical corticosteroids but the blisters lasted for a week and left behind a dark pigmentation that would take more than 6 months to fade.
Temporary henna tattooing is a custom at weddings around the world. The dyeing agent (hennotannic acid) rarely leads to skin sensitization. However, tattoo henna is often mixed with paraphenylenediamine (PPD) to hasten drying and darken the color. PPD is a common allergen found in hair dyes. Allergy to henna is rare but allergy to PPD is extremely common according to the case report authors.
Dr. Sharon Jacob, a dermatologist at UC San Diego comments: “We've seen a staggering number of people and children getting black henna . . . tattoos at local fairs, beach side stalls and cruise ships. The customers are as young as 4. Some of them have sued tattoo parlors and makers of black henna."
Many parents are unaware of the hazards of "black henna" and may unknowingly allow their children to participate in this cosmetic, novelty trend.
References:
Henna, from Wikipedia, the free encyclopedia.
In Some Henna Tattoos, a Harmful Dye. NYT.
Allergic Contact Dermatitis from a Henna Tattoo. NEJM.
Doctors warn of skin problems from black henna. Union-Tribune Publishing, San Diego.
Patch-Testing With Hairdressing Chemicals http://goo.gl/qT7xq
The use of black henna hair dye in sensitized patients can be life threatening http://bit.ly/pNytnr
Image source: Wikipedia, GNU Free Documentation License.
Image source: Wikipedia, GNU Free Documentation License.
Comments from Twitter:
@AllergyNet: Australian tourists: beware beach tattoos in Bali/Thai. Once sensitized, you cannot use perm hair dyes http://goo.gl/FJDct