If your cat has parasites, chances are he may have dandruff, too. Bites from fleas, lice and mites can all cause allergic dermatitis. One particularly nasty type, Cheyletiella mites, have been called "walking dandruff" since they're large enough to see with the naked eye but too small to distinguish detail. All skin parasites can be treated fairly easily, but in order to stamp them out completely, you'll have to treat all other animals in the home, the house itself and, sometimes, even the people. It's best to get help from your vet so you can get the most potent and fastest-working product available.
A cat's coat protects the sensitive skin underneath from the burning rays of the sun. But cats that spend a lot of time outdoors can still get sunburn, especially on the tips of their ears, eyelids, nose or lips. Any place where the hair is sparse is particularly sensitive. This is especially true of cats with white or very light-colored coats. Sunburn kills the top layer of skin, which dries up and flakes off (it can also lead to skin cancer). If you can't keep your cat indoors all the time, at least keep him indoors during the most intense period of ultraviolet (burning) sun rays -- generally from about 10:00 a.m. to 3 or 4 p.m. If your cat has a sunburn already, use a hypoallergenic lotion designed just for cats (or ask your vet for one) to help cut back on the peeling skin and dandruff.
If dry air, parasites or sunburn don't seem to be the cause of your cat's dandruff, it's time to dig a little deeper. Have you changed his food recently? Given him some "people food" that he hasn't tasted before? Used a new grooming product? Experiment with taking away the new element to see if the dandruff clears up. Your cat may also be stressed due to things like changes in the household or something as simple as new carpet. It's important to remember that cats can be sensitive to what we would consider minor changes; try to keep his environment as calm as possible.
If your cat has severe dry skin and itching, your vet may prescribe antibiotics, antihistamines or steroids to help get him feeling better. Hopefully, those little white flakes will soon be a thing of the past!