What tattoos really do to our bodies' immune systems

(CNN)I lay on the mat of the open-air bungalow in Apia, Samoa, looking up at a gecko. As its tail quivered, I felt a sympathetic twitch in my leg. Su'a Sulu'ape Paulo III, the sixth-generation Samoan hand-tap tattoo master leaning over me, paused to see if my movement was due to pain.

I'd been in Samoa for a month, studying Samoan tattooing culture and the impact of the big traditional pieces called pe'a and malu -- tatau in general -- on the immune system. Now I was getting my own hand-tapped leg tattoo, albeit considerably smaller.
This field season was the fourth of my research on the relationship between tattooing and immune response. My first study had focused on a small sample, mostly women, in Alabama. What I'd observed among that group suggested that tattooing could help beef up one's immune respo