Cold weather often brings skin problems such as dry skin. The white flakes are most likely normal cat dander (which is the stuff that causes allergies.) There are a number of commercial products available for both topical and oral treatment of dry skin.

You could also try adding a bit of oil to kitty's diet, particularly if she is eating a straight dry food diet.

Frequent brushing: two or three times a week for shorthairs and daily for longhairs, also helps in keeping dander and shedding at a minimum.

There's also a thing called walking dandruff which is a little mite. A vet needs to exam this under a microscope to see if it's this, or just normal dander.

http://www.bobmckee.com/Client%20Inf...ermatitis.html