my scratching cats

Question
I have two indoor cats and in July we had an infestation of fleas; I don't know how they got in.  I had the exterminator treat the house, twice.  Both cats were treated at the vet immediately and in a few weeks I saw no signs of the fleas.  My question is this: why are my cats still scratching, over-grooming and nipping?  It is driving me crazy to watch them.  They are both between 7 and 8 years of age; one male and one female.

Answer
Even though there are no fleas, the cats are most likely allergic to the flea bites.  Many animals can have the skin itching from flea allergy long after the fleas are gone.  Ask your vet if your cats can have a shot of DepoMedrol to help relieve the itching.