It's probably mange if the skin looks normal. If so, you have to go to the vet for treatment (a pill or cream).
Usually the skin is irritated or has discoloration from other conditions or parasites.
The good news is if it is mange, it's easily treatable.
Her skin looks very normal...no redness, no spots, no bitting, just skin underneath.
Thank you for your reply,
Snooze
It could be mange. It also could be an allergy. It could also be stress related, fur removal from excessive licking is a common cat stress behavior. It could be ringworm as well.
What's the condition of the skin where the fur has been removed. Can you describe it?