Henna tattoos can cause months of pain and discomfort and may lead to a lifelong allergy, a skin expert has warned.

Bjorn Hausen of the Dermatological Centre in Buxtehude, Germany, says the temporary "tattoos" can cause contact dermatitis in some people, making the skin swollen, red and itchy.

Mr Hausen says the problem is not the henna dye itself, but a chemical often added to make the tattoo darker. Para-phenylene diamine (PPD) is used in many industrial processes and exposure to it in a tattoo may not only harm the skin, but create hypersensitivity to the chemical. A lifelong allergy to PPD could make it impossible for the sufferer to enter certain professions.

Henna body painting is a long tradition in India, where it is called "mehndi", Morocco and Fiji. Its popularity in the West soared two years ago after Madonna had her hands elaborately decorated for her video to the song "Frozen".

Mr Hausen told New Scientist magazine: "It is possible that the mark from the tattoo will remain for several months, which is of course socially quite uncomfortable if it concerns parts of the body which are very visible, such as the hands or fingers. But above all, these tattoos can cause a hypersensitivity to PPD."

His findings appear in Deutsches Arzteblatt, the journal of the German Medical Association. Most parlours in Europe and the US use pure henna, which rarely causes allergies. But street vendors and henna artists in Third World countries pose a much bigger risk, Mr Hausen warned.