Medical tattoos are used to ensure instruments are properly located for repeated application of radiotherapy and for the areola in some forms of breast reconstruction. Tattooing has also been used to convey medical information about the wearer (e.g., blood group, medical condition, etc.). Additionally, tattoos are used in skin tones to cover vitiligo, a skin pigmentation disorder.
SS blood group tattoos (German: Blutgruppentätowierung) were worn by members of the Waffen-SS in Nazi Germany during World War II to identify the individual's blood type. After the war, the tattoo was taken to be prima facie, if not perfect, evidence of being part of the Waffen-SS, leading to potential arrest and prosecution. This led a number of Ex-Waffen-SS to shoot themselves through the arm with a gun, removing the tattoo and leaving scars like the ones resulting from pox inoculation, making the removal less obvious.
Tattoos were probably also used in ancient medicine as part of the treatment of the patient. In 1898, Daniel Fouquet, a medical doctor, wrote an article on “medical tattooing” practices in Ancient Egypt, in which he describes the tattooed markings on the female mummies found at the Deir el-Bahari site. He speculated that the tattoos and other scarifications observed on the bodies may have served a medicinal or therapeutic purpose: "The examination of these scars, some white, others blue, leaves in no doubt that they are not, in essence, ornament, but an established treatment for a condition of the pelvis, very probably chronic pelvic peritonitis."