The most common and most likely answer to this crossword clue is the 11 letter word DISTRESSING
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More clues leading to the result DISTRESSING
Buddy explains!

The straight part
We know that "Upsetting/losing one's hair?" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case upsetting/losing one's hair? = distressing.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 DISTRESSING mean?
DISTRESSING verb- To cause strain or anxiety to someone.
- To retain someone’s property against the payment of a debt; to distrain.
- To treat a new object to give it an appearance of age.
- Causing distress; upsetting; distressful.