Although the most common problem with tattoos is that people later want them removed, tattooing can also be a health hazard. Unsterilized equipment can transmit diseases such as AIDS and hepatitis. Many pigments used in tattoo inks are not approved for skin contact, much less injection. (Some are industrial-grade colours that are suitable for printers ink or automobile paint.) The pigment can migrate into unwanted areas. Some people also develop allergic reactions to the inks and some experience swelling or burning in the tattooed areas if they undergo magnetic resonance imaging (MRI).
Over the last 20 years, the number of tattoo studios in the USA has risen from 300 to more than 4,000. About half of the states now have regulations governing the practice.
In 2000, about 18 percent of US college students now have tattoos. Women now account for half of all tattoo recipients. Many people now get tattoos not as a fashion statement but to simulate natural pigmentation after breast or facial surgery, to create artificial eyebrows in certain hair loss conditions or to make discoloured skin look more normal despite a skin disease called vitiligo.
A study was made in the USA of 626 men and women who did not know their hepatitis status and came into an orthopaedic clinic for reasons unrelated to hepatitis. Nearly a fifth of participants had a tattoo. Of those who had a tattoo, 22% were infected with hepatitis C, and of those who had it done at commercial parlours (as opposed to in their own homes), 33% had the disease. Only 3% of people without a tattoo had hepatitis C.