Allergic reactions are also potential danger of tattoos and piercings. Tattoo colors are made by mixing dry pigments with a suspension fluid. More than fifty different pigments and shades are used in tattooing. Tattoo pigments can be made from a variety of materials, ranging from vegetable matter to plastic-based pigments like acrylic. Organic-based tattoo pigments are seldom reactive to human tissue; plastic-based pigments, however, are more likely to cause allergic reactions. There is no governmental oversight of these substances. Although several color additives are approved by the FDA for use in cosmetics, which are applied on the skin, the FDA does not regulate the use of color additives in the practice of tattooing, in which inks are injected into the skin.

Minor allergic reactions to the tattoo dyes typically result in an itchy rash at the tattoo site. More serious reactions included the development of granulomas, nodules that form around material the body perceives as foreign. Severe allergies can result in shortness of breath, rapid heartbeat, and fever.

Like tattoo dyes, piercing jewelry can cause allergic reactions. Brass-plated, nickel, and gold jewelry are the most likely types to cause allergic reactions. A piercing allergy often results in a weeping, itchy wound around the piercing. At times the body may react by pushing out the jewelry.