Henna, an ink from the leaves of a shrub grown in India, North Africa and Sri Lanka, is relatively safe and has been used for many years in hair dyes and temporary skin tattoos; however, according to The London Free Press, black henna ink contains paraphenlyendiamine (PPD) as an additive to darken the color, and many people become sensitized to PPD after receiving a temporary tattoo.

Dr. Joel DeKoven has treated several patients for allergies related to henna tattoos. He explains, "Subsequent exposure to PPD - even in low concentrations, such as those in hair dyes - can lead to a delayed hypersensitivity reaction."

Dr. DeKoven has seen such reactions in patients who went to hospital emergency rooms a day or two after dying their hair. Symptoms included redness and irritation around the hairline and scalp, face swelling, where the eyelids were shut, and a rash all over the body. The common link is that all previously had at least one black henna tattoo.