My cat constantly scratches her head

Question
My female cat of 7 years scratches her head a lot, specifically the patches between the ears and eyes (I guess scent glands?).  She scratches herself until she bleeds sometimes.  I've switched to non-perfumed litter thinking she may have allergies.  I give my cats Frontline for cats to keep bugs at bay so I don't think she has those; my other two cats don't seem to be bothered.  She doesn't seem to be in pain and it's not a constant thing, but I'm worried.  I've put cortisone on her a few times, but she doesn't like that.  What else can I try?

Answer
When cats scratch that area I think of two possibilities.  One is ear mites, so you need to have that checked. The other is a sensitivity to a component of her food.  Cats with food allergies will tear up their faces from the intense itching. Sometimes changing to a different food will stop the itching.