Allergic reactions to henna-based temporary tattoos and their components.

Temporary henna-based tattoos, particularly popular among western tourists holidaying in exotic places, can expose to the risk to develop allergic reactions. Although hypersensitivity to henna is extremely rare, para-phenylenediamine, which is sometimes added to henna to obtain a dark, blackish color, is a frequent contact sensitizer. The purpose of this article is to review the literature about allergic reactions to temporary henna tattoos and outline the causes, clinical aspects and complications of this practice that should not be regarded as innocuous and risk-free.