A medical tattoo is a tattoo used to show the illnesses or allergetic reactions one has. Medical tattoos can be used for a number of reasons:

• As a warning that a patient suffers from a chronic disease that can exacerbate suddenly and that will require immediate specialist treatment. One example is in the case of congenital adrenal hyperplasia, in which patients may need steroid replacement therapy during ordinary illness.

• As an aid in radiotherapy. In order to minimize damage to surrounding tissues, the radiotherapist seeks to keep the irradiated field as small as possible. Marking a number of points on the body with tattoos can aid radiotherapists in adjusting the beam properly.

• During breast reconstruction after mastectomy (removal of the breast for treatment of cancer), or breast reduction surgery. Tattooing is sometimes used to replace the areola which has been removed during mastectomy, or to fill in areas of pigment loss which may occur during breast reduction performed with a free nipple graft technique.