Health Risks of Tattoo

 A tattoo is made by inserting indelible ink into the dermis layer of the skin to change the pigment. Tattoos on humans are a type of body modification, and tattoos on other animals are most commonly used for identification purposes
Because it requires breaking the skin barrier, tattooing may carry health risks, including infection and allergic reactions. Modern tattooists reduce such risks by following universal precautions, working with single-use items, and sterilizing their equipment after each use. Many jurisdictions require that tattooists have blood borne pathogen training, such as is provided through the Red Cross.
In amateur tattoos, such as those applied in prisons, however, there is an elevated risk of infection. Infections that can theoretically be transmitted by the use of unsterilized tattoo equipment or contaminated ink include surface infections of the skin, herpes,simplex virus, tetanus, staph, fungal infections, some forms of hepatitis, tuberculosis, and HIV. In the United States there have been no reported cases of HIV contracted via commercially-applied tattooing process.
Tattoo inks have been described as "remarkably nonreactive histologically". However, cases of allergic reactions to tattoo inks, particularly certain colors, have been medically documented. This is sometimes due to nickel in an ink pigment, which is a common metal allergy. Occasionally, when a blood vessel is punctured during the tattooing procedure a bruise may appear.