It could be mites or dry skin or a mix of both.
With mites they tend to itch a lot, sometimes the bulb (ball at the end if the quill) will be chewed off. You can do a check on a black materal, rub their back and see if the flakes move on their own after.
You can to a vet and say you susspect mites and then treat for that.
Adding a little flaxseed oil to food twice a week helps with dry skin which is a common problem with them.