Irish tourists who avail of temporary henna 'tattoos', may end up with long term skin problems, scientists have warned.

Painting henna designs on the body is a long-established practice in some parts of the world. However in recent years, street stalls offering henna 'tattoos' have become big business in sun resorts all over the world.

Most parlours offering this service use pure henna, which very rarely causes skin reactions. However street vendors may add a chemical called PPD (para-phenylene diamine), in order to make the tattoos appear darker.

Henna containing PPD can cause contact dermatitis in some people, according to scientists at the Dermatological Centre in Buxtehude, Germany.

It is also possible that the mark from the tattoo will last for several months, they claim. Henna tattoos are supposed to last for no more than two weeks.

Their findings appear in the journal of the German Medical Association and 'New Scientist' magazine and the association now intends to launch a Europe-wide campaign to warn people, especially tourists, of the risk.