The risk of spreading infection through the use of unsterilized needles during tattooing has been known for decades. Now, health experts are warning that the pigmented ink used for tattoos could contain carcinogenic substances and heavy metals.

“Unfortunately, serious risks will sometimes be revealed on products once thought to be safe,” commented Daniel Nigh, a product liability lawyer with the Levin, Papantonio law firm. “Since tattoos are so common, this could prove to be a serious health issue for many people.”

Researchers at Bradford University in the United Kingdom found that tattoo inks containing nanoparticles of carcinogenic substances subsequently damaged collagen, an essential protein found in the body, The Sunday Times reported.

Contrary to popular belief, tattoo ink pigments have not been regulated by the U.S. Food and Drug Administration (FDA). In December 2013, the FDA issued a consumer update concerning the risks of using tattoo ink for body tattoos, temporary tattoos, henna, and permanent makeup, with the agency warning that pigmented tattoo inks can become contaminated with bacteria, mold, and fungi.

According to the Times of India, nearly 5 percent of tattoo studios are believed to use ink that contains carcinogenic substances, including heavy metals such as cobalt and mercury. The Natural News reported that mercury, lead, antimony, beryllium, cadmium, and arsenic have also been found in tattoo ink.

Heavy metals can be toxic to the body, and their presence in the bloodstream can have detrimental effects. Long-term exposure to mercury can damage the nervous system, causing physical and emotional disorders. Lead is toxic to the heart, bones, intestines, and nervous system, and lead poisoning can lead to adverse health events, such as seizures, coma, and death.

In addition to carcinogens and heavy metals, traces of hydrocarbons and phthalates have also been found in tattoo ink. In animal studies, phthalates have been observed to cause damage to animal kidneys, lungs, liver, and reproductive system. Even worse, dissolving tattoo ink in the skin with laser treatments – a common form of tattoo removal – can release these harmful substances into the bloodstream.

Experts are advising that leaving a tattoo in place may potentially be safer than removal, as harmful substances could be present in the ink.

Krysta is a writer and researcher with Ring of Fire. Follow her on Twitter @KrystaLoera.