Using a database that tracks the health outcomes of twins, scientists have found more evidence that getting tattoos may be linked to skin cancer.
In a new paper published in the journal BMC Public Health, researchers from the University of Southern Denmark and Finland's University of Helsinki have found that among twins, tattooed individuals are roughly 1.62 times more likely to develop skin cancer than their un-inked siblings.
Looking at data on more than 2,600 twins, the Danish scientists found that this link was even greater for people who had larger tattoos, defined as larger than palm-sized. The twins with bigger pieces were found to have skin cancer roughly three times more often than their siblings without tattoos.
(Though it's not related explicitly to tattoos, it is worth noting that Denmark has some of the highest rates of skin cancer in the world. Because the small Scandinavian country is located so far from the equator, its residents don't get the same amount of solar radiation as their counterparts further south, and often get worse cancer-causing sunburns as a result.)
While it's fairly well known that tattoo ink is often toxic due to the lack of regulation for the industry that produces it, it's still relatively unclear exactly how affects the human body — especially because researchers can't seem to decide what biological mechanisms it impacts.
In this new study, the scientists rely upon prior research that found tattoo ink particles migrating and accumulating in the lymph nodes. As such, the researchers included lymphoma, a disease that targets the immunity-regulating lymphatic system, in the cancers they were on the lookout for.
"When tattoo ink penetrates the skin, some of it is absorbed into the lymph nodes," a press release from the school explains. "The researchers are particularly concerned that tattoo ink may trigger chronic inflammation in the lymph nodes, which over time could lead to abnormal cell growth and an increased risk of cancer."
In the school's statement, hematologist and clinical professor Henrik Frederiksen suggested that it's possible our bodies attack tattoo ink particles that enter the lymph nodes because they're perceived as "foreign substances" that need to be expelled.
"This may mean that the immune system is constantly trying to respond to the ink," the press release theorizes, "and we do not yet know whether this persistent strain could weaken the function of the lymph nodes or have other health consequences."
As with all other studies of this nature, these Danish scientists acknowledge that there needs to be much more research to fully figure out if, how, and why tattoo ink can be substantially linked to cancer. While there has been lots of research that found people with tattoos seem to be diagnosed with skin cancers more often than their un-tattooed peers, it's still a big question mark as to why that might be happening.
On their part, the Denmark-based team behind this study plans to study tattoo inks' effects on the lymph nodes "at the molecular level" — and to see if certain types of lymphoma are more associated with tattoos than others.
More on foreign substances: Microplastics Getting Stuck in Brain Vessels Like Clots, Scientists Find, Causing "Neurological Abnormalities" in Mice
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