I've known cats to pull out their own fur due to a variety of reasons.A lot of the time it can be put down to stress which exhibits itself as excessive licking. Also hormonal disease are responsible for some hairloss. The treatmant is usually the same for both & that is hormonal therapy which has a calming effect & also reduces the irritation if it's an allergy.
A Vet would be able to see under a microscope if the hairs are being pulled out (there would be visible broken hair shafts) or are falling out on their own (when you'd be able to see normal growing hair tips)
Ringworm is another thing that causes bald patches.
You must seek proper advise tho, get some skin scrapings sent off & check the cats blood.
My cat is doing the same thing.
He seems to be washing excessively on his stomach & between his legs.
This has resulted in a rather large bald patch.
As soon as it starts to grow back he removes it again.
My vet has checked him over & said there's no problem, he just likes to be very clean.
Cats tend to pull out their fur when they have dry skin or stress. I would suggest you change the brand of cat food you use, try to fine out what is upsetting the feline, or take it to the vet (if all else fails put a cone on it).