The researchers discovered that once a tattoo is made, the ink rapidly travels through the lymphatic system and, within hours, accumulates in large quantities in the lymph nodes — key organs of the body’s defense system. Inside these nodes, immune cells called macrophages actively capture all types of pigment. This ink uptake triggers an inflammatory response with two phases: an acute phase lasting about two days after tattooing, followed by a chronic phase that can persist for years. The chronic phase is particularly concerning because it weakens the immune system, potentially increasing the susceptibility to infections and cancer. The study also showed that macrophages cannot break down the ink like they would other pathogens, wich causes them to die, especially with red and black inks, suggesting these colors may be more toxic. As a result, ink remains trapped in the lymph nodes in a continuous cycle of capture and cell death, gradually affecting the immune system’s defensive capacity.

Finally, the research explored a question raised during the COVID-19 pandemic: could receiving a vaccine in a tattooed arm affect vaccine efficacy? The study found that tattooed mice produced significantly lower levels of antibodies after vaccination. This effect is likely due to the impaired function of immune cells that remain associated with tattoo ink for long periods. Similarly, human immune cells previously exposed to ink also showed a weakened response to vaccination.