The most common and most likely answer to this crossword clue is the 8 letter word DANDRUFF
I've seen this crossword clue in Financial Times
D
A
N
D
R
U
F
F
More clues leading to the result DANDRUFF
- Flecks from toff's brief neckwear?
- Scales down, at the outset, original RAF fund
- Jacob’s son died, with collar showing one sign of dermatitis
- Last thing you want in head and on collar?
- What may be seen, when scurvy knaves are collared
- Ultimately cod as well as other fish shedding scales
- Daughter with pronounced coarse hair problem
- Democrat with Trump effecting flaky fallout
Buddy explains!

The straight part
We know that "sign of dermatitis/collar" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case sign of dermatitis/collar = dandruff.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.
What does DANDRUFF mean?
DANDRUFF noun- Scaly white dead skin flakes from the human scalp; Pityriasis capitis.
- To fall or cover with white flakes, like dandruff.