Skin eruption (4)
I believe the answer is:
rash
'skin eruption' is the definition.
(I know that rash is a type of skin eruption)
This is all the clue.
(Other definitions for rash that I've seen before include "Red patch on skin" , "Hotheaded" , "Flood" , "Eruption on skin, imprudent" , "Precipitate" .)