The most common and most likely answer to this crossword clue is the 7 letter word SHAMPOO
I've seen this crossword clue in The Guardian
S
H
A
M
P
O
O
More clues leading to the result SHAMPOO
- Utensil finally wiped, meat assumed to be cleaner
- Current measure in Soho upset cleaner
- Bathroom purchase fake? Not entirely dreadful
- Hair product, counterfeit and low quality, not finished
- Meat in spoon finally wiped to be cleaner
- Cleaner, fake, not entirely substandard
- Go away carrying current bathroom cleaner
- Wash plastic turd?
- Largely counterfeit toiletry
- Start to smoke joint and smell clean hair
Buddy explains!

The straight part
We know that "clean hair" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case clean hair = shampoo.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 SHAMPOO mean?
SHAMPOO noun- A traditional Indian and Persian body massage given after pouring warm water over the body and rubbing it with extracts from herbs.
- A commercial liquid soap product for washing hair or other fibres/fibers, such as carpets.
- An instance of washing the hair or other fibres with shampoo.
- Champagne.
- To wash one's own hair with shampoo.
- To wash (i.e. the hair, carpet, etc.) with shampoo.
- To press or knead the whole surface of the body of (a person), and at the same time to stretch the limbs and joints, in connection with the hot bath.