The most common and most likely answer to this crossword clue is the 4 plus 6 letter word FLEA COLLAR
I've seen this crossword clue in The Guardian
F
L
E
A
C
O
L
L
A
R
More clues leading to the result FLEA COLLAR
Buddy explains!
The straight part
We know that "All clear of rash — with this" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case all clear of rash — with this = flea collar.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.