Track it
What it can look like. A general, vet-reviewed example — signs vary and this is not a diagnosis. When in doubt, ask your vet. 
Flaking & dandruff in dogs
Clinical name: Scaling / seborrhea
Dry flakes in the coat and a dull look to the fur.
Where it shows upback · trunk
Typical patternAlong the back and trunk.
Linked allergy typesEnvironmental (atopy) · Food allergy
Food vs environmentalNon-specific.
What you can do
Track it alongside other signs; flaking alone is rarely urgent.
Don't confuse it with
Other causes a vet will want to rule out: dry air, Cheyletiella mites, poor diet.
This is educational information, not a diagnosis or treatment plan. Always see your veterinarian about your dog's health.
Related signs
Hot spotsSee your vet
A moist, red, oozing and painful patch that appears fast, with hair loss over it.
Pus-filled spotsKeep an eye on it
Small pimple-like spots with a white/yellow head.
Crusts & scabsKeep an eye on it
Dried serum or blood forming crusts and scabs, often where the dog has scratched.
Scratch woundsKeep an eye on it
Raw, broken skin and scratch marks from the dog's own claws.