Hair treatments for pools punters? (5)

I believe the answer is:
perms
'pools punters?' is the definition.
Although both the answer and definition are plural nouns, I don't see how they can define each other.
'hair treatments' is the wordplay.
'hair' becomes 'perm' (perm is a kind of hair).
'treatments' becomes 's' (I can't explain this - if you can you should give a lot more credence to this answer).
'perm'+'s'='PERMS'
'for' acts as a link.
Can you help me to learn more?
(Another definition for perms that I've seen is " Hairdos".)
