Scientists have reported a possible correlation between having tattoos and getting lymphoma later in life. However, multiple caveats apply [1].
Looks cool, but what about safety?
Tattoos are a popular form of self-expression, and in recent years, they are becoming more prevalent, probably due to the loosening of social taboos. Current, effective techniques of tattoo removal also encourage people to get one because they don’t feel it’s permanent. However, tattoos are, in essence, an invasive procedure that involves being injected with various chemicals of questionable regulation. Hence, questions about health effects of tattoos are quite valid, and they are indeed abundant online. Amazingly, there is very little actual research that looks into that.
In a new study, researchers from the Lund University in Sweden leveraged their country’s robust system of medical records to shed some light on the issue. Among the people who had completed a vast medical questionnaire in 2021, they picked out all the cases of lymphoma and added three age- and sex-matched controls to each one. This design is known as a “matched case-control study.”
The researchers then looked at how cases of lymphoma correlated with tattoos in people aged 20-60, when this disease is the most prevalent. Lymphoma is a cancer of the lymphatic system that, unlike many other types of cancer, affects many young people. However, it is also one of the least deadly cancers.
A possible connection
At the beginning of their paper, the authors offered a tentative explanation to the possible link between tattoos and lymphoma. Tattoos are made using a cocktail of inks that may contain compounds such as primary aromatic amines (PAA) and polycyclic aromatic hydrocarbons along with toxic metals, including arsenic, chromium, cobalt, lead, and nickel. “A significant and concerning number of them,” according to the paper, are classified as carcinogens [2].
“We already know that when the tattoo ink is injected into the skin, the body interprets this as something foreign that should not be there and the immune system is activated,” said Christel Nielsen, the lead investigator. “A large part of the ink is transported away from the skin, to the lymph nodes where it is deposited.”
21% increase in risk
After controlling for several confounding variables, including sex, age, educational attainment, smoking status, hazardous occupation, and taking immunosuppressive drugs, the scientists found that people with tattoos had 21% more risk of getting a lymphoma. However, there is a lot to unpack in this result.
Most glaringly, it did not quite reach statistical significance, with a p-value of 0.067 (the commonly used threshold is 0.05). In matched case-control studies, the two main types of analysis are matched and unmatched. In the former, the matching that is performed at the design stage, where each case was matched to one or more controls, is preserved at the analysis stage. This controls better for possible confounding variables, but it also weakens the statistical power and widens the confidence interval. Still, it is considered the golden standard in such studies.
Unmatched analysis ignores the design-stage matching, increasing the statistical power but weakening the control over possible confounders. In this study, the fully adjusted unmatched analysis showed a statistically significant (p=0.04) 18% increase in the risk of lymphoma for people with tattoos.
Is removing tattoos even less safe?
The study reports several other interesting results. Most importantly, no correlation between lymphoma incidence and the overall tattooed area size was found. This surprised the researchers, who offered a following possible explanation: since there were usually several years between the time of assessing the tattoo status and the time of the lymphoma diagnosis, it is possible that during that time, some respondents acquired more tattoos, which would lead to misclassification. However, another possible explanation, Nielsen said, is that “a tattoo, regardless of size, triggers a low-grade inflammation in the body, which in turn can trigger cancer.”
Alarmingly, laser removal of tattoos showed an even stronger positive correlation with lymphoma incidence. Speculating about possible causes, the researchers cite reports that certain compounds in tattoo inks can be transformed by laser irradiation into other, more carcinogenic, compounds [3].
This study is the most rigorous to date to analyze the possible link between tattoos and lymphoma, but its findings are far from definitive. In addition to the questionable statistical significance of the results, populational studies can only demonstrate correlation but not causation. As the authors themselves note, more rigorous studies are needed. However, it is also common sense that having tattoos is less safe than not having them.
Literature
[1] Nielsen, C., Jerkeman, M., & Jöud, A. S. (2024). Tattoos as a risk factor for malignant lymphoma: a population-based case–control study. EClinicalMedicine, 72.
[2] IARC Working Group on the Evaluation of Carcinogenic Risks to Humans. (2010). Some non-heterocyclic polycyclic aromatic hydrocarbons and some related exposures. IARC Monographs on the evaluation of carcinogenic risks to humans, 92, 1.
[3] Hauri, U., & Hohl, C. (2015). Photostability and breakdown products of pigments currently used in tattoo inks. Curr Probl Dermatol, 48, 164-169.
