I always wondered about this. I assumed "surely there must be loads of studies on what happens if a person's back, arms and thighs are covered in colorful tatto

I always wondered about this. I assumed "surely there must be loads of studies on what happens if a person's back, arms and thighs are covered in colorful tattoos, because nature didn't design us to do this by default". Nature also didn't design us to wear socks, but that seems mostly harmless. I just always wondered about putting ink permanently in skin. People get exotic glow in the dark tattoo ink. That seems nuts to me.