My chihuahua has a terrible time scratching, she is losing hair , her skin looks red and irritated and has developed some hot "itchy spots she scratches and makes a sore. I have tried changing her brands of food, Any ideas?? :confused:

Fleas?

Chances are, it is not the food. In some cases, dogs do develop allergies. In that case, you need to change the protein source. If your dog is allergic to Lamb, switching from Pro Plan Lamb to Iams Lamb won't help. You would need to change to beef or chicken. Pick a chow and stick to it.

How often are you bathing it? The less the better. If you don't rinse the last little bit of shampoo out, it will irritate the skin.

Could be food, but I would first check that she is on a vet product for fleas. It could be several other medical issues as well i.e.. Mange, thyroid. How old is she?