Unprotected skin in long finger (6)
I believe the answer is:
pinkie
'finger' is the definition.
(pinkie is a kind of finger)
'unprotected skin in long' is the wordplay.
'unprotected' says to take the centre.
'in' means one lot of letters goes inside another.
'long' becomes 'pine' ('pine' can be a synonym of 'long'**).
The central letters of 'skin' are 'ki'.
'ki' going within 'pine' is 'PINKIE'.
(Other definitions for pinkie that I've seen before include "The little finger in America" , "An American little finger" , "Smallest digit" .)