Stay calm to avoid sunburn perhaps (4,4,5,2)
I believe the answer is:
keep your shirt on
'stay calm' is the definition.
'to avoid sunburn perhaps' is the wordplay.
I cannot really understand how this works, but
'to' is within the answer.
'perhaps' could be 'y' (I've seen this in other clues) and 'y' is located in the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for keep your shirt on that I've seen before include "remain cool" , "don't panic!" , "Not topless please" , "Avoid exposing body to sun's rays" , "Chill out!" .)