Tanning pigment (7)
I believe the answer is:
melanin
'tanning pigment' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for melanin that I've seen before include "Tanning pigment in skin" , "Light-absorbing skin pigment" , "Pigment that accounts for skin colour" , "Dark skin pigment" , "Brown skin pigment" .)