A tattoo in the most common sense is a picture, figure or text drawn in ink (or other pigment) under the topmost layer of skin on an animal or human. In modern times the ink is introduced under the skin by a needle, although some tribal cultures create them by cutting and then rubbing the wound with ink, ashes or other agents. This was probably the original method.
The purposes of tattoos are diverse. Identification, cosmetic, religious and magical uses are the most common. The most horrid use ever made of tattoos is probably the identification of Jews during the Holocaust.
Tattooing has been used for thousands of years, as evidenced by Oezti.
Temporary tattoos made with 'black henna' may cause allergic reactions. 'Black henna' is fabricated by adding PPD (p-Phenylenediamine) to natural henna, in order to achive a black color rather than the orange through brown stain of natural henna. PPD is very unhealthy .