The harmful effects of tattoos on the immune system

When you tattoo your skin, you also "tattoo" your immune system. This is the finding of an innovative study conducted by the Infection and Immunity group at the Institute for Research in Biomedicine (IRB), affiliated with Università della Svizzera italiana (USI), led by Prof. Santiago F. González and published today in Proceedings of the National Academy of Sciences (PNAS), one of the world's most prestigious scientific journals.

Although tattoos are now very common – it is estimated that one in five people has at least one – the scientific community still knows little about the potentially toxic effects of the pigments used, particularly their interactions with the immune system. The new IRB study, conducted in collaboration with 12 international groups and the result of seven years of research, analysed the path of ink in the body using animal models and human samples, focusing on the three most commonly used colours: black, red and green.

The ink quickly reaches the lymph nodes

The researchers found that after a tattoo is applied, the ink rapidly migrates through the lymphatic system and accumulates in large quantities in the lymph nodes within a few hours. Here, immune cells called macrophages capture all types of pigment, triggering a two-stage inflammatory response: an acute phase lasting about two days and a chronic phase that can persist for years.

This prolonged inflammation can weaken the immune system and raise vulnerability to infections and tumours. The study also highlights that macrophages are unable to break down the ink, leading to their death, especially in the presence of red and black pigments, suggesting that these colours are more toxic. The result is a continuous cycle of pigment acquisition, cell death and further accumulation of ink in the lymph nodes.

Tattoos and vaccine response

The study also explores a question that emerged during the COVID-19 pandemic: does having a tattoo affect the effectiveness of a vaccine? In the analysed animal models, tattooed mice exhibited significantly lower antibody levels after vaccination. Similar effects were also observed in human immune cells previously exposed to inks, which showed reduced immune responses.

New research perspectives

The results raise important questions about the safety of tattoos and the possible link between chronic inflammation caused by inks and other diseases, such as cancer or autoimmune diseases. Further studies will be needed to broaden our understanding of these phenomena and define safer procedures for an increasingly widespread practice.