My cat started just to lose clumbs of hair and I saw a flea on him, so I got a flea collar. Then he just started to lose all of his form his tail to his mid-back. So I took the collar off. Now he hasn't been losing his hair as much, but it is not growing back. Could he sick from something or could it be stress? We do have three dogs and this never happend with the oldest, it all started when we brought the new ones home.
A few ideas for you:
First of all, if your cat is older than 7, he should be evaluated by a vet and have bloodwork done to check for an internal disease that may be causing the problem. Hyperthyroidism in particular can cause hair loss. This is a common disease in older cats and is readily treatable with medication.
If he is a younger cat, then this is most likely a reaction to the fleas. He may even be allergic to flea bites. First of all, forget about flea collars - fleas are now resistant to the medication in the collars and the collars themselves can cause a reaction in a sensitive pet. Same goes for powders and sprays.
There are newer products available to treat fleas - Advantage, Frontline, and Revolution are all flea preventatives that are in the form of drops that go on the back of the neck once a month. They are available from a veterinarian only. Please avoid over the counter flea drops, as they are not as effective and are toxic to some cats.
It is worth the trip to the vet to get the flea products, as you can have your cat's skin examined at the same time to make sure he doesn't need an antibiotic totreat a secondary skin infection or a steroid to treat a suspected allergy.
I hope this helps you,