Tattoos: Unlikely but Plausible Friends of the Immune System

“Humans have marked their bodies with tattoos for thousands of years. These permanent designs—sometimes plain, sometimes elaborate, always personal—have served as amulets, status symbols, declarations of love, signs of religious beliefs, adornments and even forms of punishment.”

Until a few decades ago, the earliest known tattoos were those found on several Egyptian female mummies dated to 2000 B.C. However, the discovery of the Ötzi, an ancient mummified human body found by a German tourist on the Italian-Austrian border in 1991, provided the first evidence that tattoos have been around for more than 5,000 years. Using imaging techniques, anthropologists have mapped 61 tattoos on the mummified Ötzi. The tattoos were made by piercing the skin with a needle, and then rubbing charcoal into it—“and they still look pretty darn good, all things considered.”

Since then, not much has changed. Permanent tattoos are now made by inserting pigments through pricks into the dermis, the lower part of the skin—usually using a hand-held tool that acts similarly to a sewing machine. One or more needles pierce the dermis repeatedly, as many as 200 times per second, opening a void that sucks in the ink while the needles lift out of the skin.

Because the practice of tattooing damages the skin, it challenges the immune system, making people more susceptible to infection. “Once the ink is deposited, there is an inflammatory response that surrounds the ink particles and creates a matrix that allows the ink to stay and not migrate or disappear on its own. It’s inflammatory cells that surround the ink and allow it to stay put.”

The ink is likely picked up by the skin macrophages, and it dwells in these cells for their entire lifespan.

“But much of tattooing remains mysterious: Scientists still aren’t sure what makes certain tattoos fade fast, why others stick around when they’re supposed to disappear, or how they react to light. One of the strangest and least-studied enigmas, though, is how tattoos survive at all. Our immune system is constantly doing its darndest to destroy them—and understanding why it fails could clue us in to one of our bodies’ most important functions, even when we leave the skin blank.”

A study published last week (April 3, 2023) in the American Journal of Biological Anthropology, shows that tattooing increases innate immune activity. The authors view tattooing as a phenotypic gambit. As they explain it, a gambit is the sacrifice of something to gain an advantage. What about the phenotypic gambit, then? It’s the development of traits or behaviors that occur at high rates as part of a refining process of natural selection. Although this process may at first appear costly, it might eventually lead to advantages. For tattooing, it could be increased immunological health deriving from the stimulation of the immune system.

For the study, investigators assessed innate functional immune responses by determining the bacteria-killing activity of saliva samples collected from study participants before and after they received a new tattoo, taking into consideration the extent of body areas covered by tattoos and how many times the study participants underwent tattooing. They found that the dermal stress of tattooing resulted in increased bacteria-killing activity, thus suggesting that people with more exposure to tattoos have a relatively more immediate and active immune response than those with less exposure to tattooing. The investigators conclude that tattoos may elevate innate immunological vigilance, which in turn may protect against future dermal damage.

Interestingly, “It’s also possible—though not yet borne out by data—that learning to coexist with tattoo ink could help immune cells calibrate their reactions to other substances, perhaps even heading off autoimmune attacks.”

Even if turns out that tattoos themselves do not have major impacts on the immune response, they might inspire technology able to boost it. Back in 2008, a Reuters article subtitled “The tattoo of the future may be good for your health rather than just your image” described a study by German investigators. Their research indicated that, in mice, tattooing was a more effective way to deliver a new generation of experimental DNA vaccines than standard injections into muscle. Moreover, a recent study shows that a novel intradermal tattoo-based injection device enhances the immunogenicity of plasmid DNA vaccines. Tattoo-needle techniques may therefore become an effective approach to administer vaccines.