Each of the lymph vessels within the dermis will eventually connect into a terminal swelling. We have many of these lymph nodes scattered throughout our bodies, but there is a high concentration of them at the top of our limbs, in the groin and armpit in particular. At these sites they act a bit like a sink trap in a shower that collects hair: as the ink molecules are too big to pass through the nodes, the dye accumulates there. Which is why, in people with tattoos, the nodes eventually take on all the colours of the inks.
