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.
Human subjects are crazy to work with for a few reasons
Laboratory mice literally live 5 to a cage with almost no diet variability, in a controlled environment. Yes shit does happen with research mice, but it’s something that is easy to control overall.
And yet, we manage to have hundreds of thousands of studies written about humans with human subjects. This sounds like a boatload of excuses that could be summed up as "science is hard". Sure, it's hard, but it's better than putting out a flawed study that can't scale properly.