The most common and most likely answer to this crossword clue is the 7 letter word FACIALS
I've seen this crossword clue in The Guardian
F
A
C
I
A
L
S
Buddy explains!

The straight part
We know that "Beauty treatment" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case beauty treatment = facials.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 FACIALS mean?
FACIALS noun- A personal care beauty treatment which involves cleansing and moisturizing of the human face.
- A kind of early silent film focusing on the facial expressions of the actor.
- (in some contact sports) A foul play which involves one player hitting another in the face.
- A sex act of male ejaculation onto another person's face.