Protective layer combined spermicide with extract of carbon (9)

I believe the answer is:

epidermis

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'protective layer' is the definition.
'epidermis' can be an answer for 'layer' (epidermis is a kind of layer). I'm unsure of the 'protective' bit.

I don't understand how the rest of the clue works.

Can you help me to learn more?

(Other definitions for epidermis that I've seen before include "Outer layer of skin" , "Outermost layer" , "Protective covering" , "Surface of the skin" .)

I've seen this clue in the Sydney Morning Herald.

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