Tattoo juice can stain the skin because it contains a substance called genipin, which exists in the fruits of genipin plants in the United States, and the content of genipin in Gardenia, which is rich in Jiangxi, China, is about three times that of genipin fruits.
Genipin reacts with amino acids and proteins in skin keratinocytes to produce gardenia blue pigment, which makes the skin appear blue-black, so fruit juice tattoo can also be called gardenia blue tattoo. There is a special gardenia blue tattoo cream on the market.