“Getting a new tattoo triggers your immune system to send white blood cells called macrophages to eat invaders and sacrifice themselves to protect against infection. Your body also launches what immunologists call adaptive responses. Proteins in the blood will try to fight and disable specific invaders that they recognize as problems.” Professor Christopher Lynn heads to Apia, Samoa to untangle tattoos’ influence on immune response. “Regular exercise provides immune function benefits through repetition, not necessarily single visits to the gym. We think this is similar to how each tattoo seems to prepare the body for vigilance.” (Editor’s note: I’ve never met a Samoan who needed extra protection.)