An opening in dermatology, I think (4)

I believe the answer is:

pore

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'think' is the definition.
(poring is a kind of thinking)

I cannot understand how the rest of the clue works.

(Other definitions for pore that I've seen before include "Minute opening in the skin" , "Small skin orifice; study" , "Skin opening; look closely (over)" , "Where sweat appears" , "Sweat-gland opening" .)

I've seen this clue in the Evening Standard.

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