Face full of sweat? Call for help (8,6)

I believe the answer is:

distress signal

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'call for help' is the definition.
(I've seen this in another clue)

'face full of sweat?' is the wordplay.
I cannot quite understand how this works, but
'sweat?' could be 'stress' (stress is a kind of sweat) and 'stress' is found in the answer.
This explanation may well be incorrect...

Can you help me to learn more?

(Another definition for distress signal that I've seen is " indication that urgent help is needed".)

I've seen this clue in The Sunday Times and The Times.

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