Is the cat overly scratching different parts of his/her body?  That would be
the first sign of fleas.  If you have a good magnifying glass, it is
somewhat easy to tell the difference of flea eggs and dandruff.  Dandruff is
usually always flat as a pancake whereas flea eggs are not.  I have a gut
feeling it is dandruff, otherwise, if the cat was doing an overly amount of
scratching, you would already know the probable answer.  Oh! I said that at
the start, right?  I'll also bet the cat has very dark fur.

Rich
--

My vet  simply puts the sheet of white paper under a cat, then rubs the cats
furr over it. If the cat has fleas, the flea dirt-black- will show on the
paper straight away. With some luck you may be able to even see some live
flea. Also black, but visible and bigger then flea dirt.

It sounds like it could be 'dander' ~ cat dandruff basically ~ which is
sometimes caused by too little oils in the diet and/or too little grooming
at a time when the coat is going through seasonal changes.

My vet suggested olive oil! Honestly!! Just drip a drop or two into the palm
of your hand, rub your hands together to disperse it them rub it gently over
the affected parts. The idea being that the cat links it off when washing!
If you're not happy doing that, pop a little of the paws or mix a drop in
the food. (By the way, don't use too much or the cat gets running, smelly
poo) It works particularly well after brushing if you dip your fingers into
the oil and rub it as close to the skin as poss. ~ as long as it's not
dripping off your fingers...for the above reason!!

Cats have this 'dander' all the time, it's just usually too fine to see.
Apparently it's one of causes of allergies to cat lovers ~ so if you've
anyone around who suffers from allergies who's recently flared up, this is
probably the cause.

Hope this helps!

Meant to say...can also be caused by central heating!!