The top of my list in cats is always flea allergy dermatitis, especially if the areas of the skin involved are the neck and/or lower back and tail base. It is important to make sure you are using a flea product appropriate for her weight. Even though you cannot see any fleas on her doesn't mean there aren't one or two lurking and oftentimes this is all it takes for a cat with flea allergy dermatitis. These guys are allergic to the flea's saliva so it only takes one flea to bite to set off the allergic response.
Once the allergy is under way (i.e. she gets the sores) she may require antiinflammatories (and possibly antibiotics if the sores have got infected) as well as flea treament to break the itch-scratch cycle. In the long-term flea allergies are avoided by strict flea control - every 3 - 4 weeks with Advantage or Advocate or every 5-6 weeks with Frontline. You must also ensure all dogs and other cats, in the household are treated at the same time. Very sensitive animals may also require periodic long-acting steroid injections.
Another possible cause of these symptoms is food allergy (but much less likely). To rule out a food allergy, you need to undertake a food trial with a 'hydrolysed protein' diet such as Hill's Z/D low allergen and this needs to be fed SOLELY for 3 weeks minimum to see a response. Cats can develop intolerance to a diet they have been fed for a long time, so a diet change is not a necessary precursor. After this time if you are seeing a change in your cats symptoms you can slowly introduce different foods week by week with the guidance of your Veterinarian.
It is also possible (but again much less likely) that your girl may have skin mites or lice as they commonly cause intense itching and irritation. Usually a Veterinary check up for a skin problem involves physical examination and a skin scrape to check for mites and lice, as well as signs of fleas.
There are a few things you can do in the meantime to help alleviate her itching:
- a medicated shampoo (these often require 10 minutes in-contact time which can be very difficult with cats)
- if only a small area is affected you can apply Neosporin cream sparingly twice per day.
However, it is very important for all skin problems to determine the cause before further treatment is begun.
Hope this helps,