UV tattoos or blacklight tattoos are tattoos made with a special ink that is only visible under a blacklight. The tattoos can be completely invisible in normal light. A UV tattoo becomes visible under blacklight, when it glows in colors ranging from white to purple, depending on the ink chosen. Colored ink is also available. Some people have had reactions to ingredients in the ink, ranging from minor itching to dermatitis. Several UV inks are suspected carcinogens and allergens and at this time, no research has been conducted into the possible side effects of long term exposure. Some UV inks are known to yellow or turn slightly brown with sun exposure. UV inking takes a little bit longer than normal, due to UV inks being a little thinner and harder to work with, and because the tattoo must be wiped and checked under a blacklight frequently during application.