Deedlit has allergic dermatitis and it is mostly enviromentally factored, it doesn't bother her much in the winter but summer is here and now she is itching and making the hotspots. When we lived in SC it was really bad and she actually made bloody sores and had to be on antibiotics they were so bad. The vets there did get me to give her an allergy shot (steroidal) but I really didn't like to, steroids have been known to cause side effects and even major problems if used over a long period of time. IMO the allergy shots helped Deedlit somewhat, but always temporary, so I chose to keep her off them when we moved back to IL and to just try to keep her comfy during the summer months which is is when they flare up. Hers started when she was about 2 or 3 years old too. Things that can help are switching to a good food (NO CORN), using a medicated or soothing shampoo, giving baths more often, I usually only bath my chis once a month or so but with allergies it can provide relief to do it more often, and also a fatty acid supplement or oil for her food could help. Allergies are a bath thing to fight, this is going on three years now with Deedlit but I think we're finally getting to a control point. Hope that's helpful.
Here is a site with some good info:
~*~Gypsy, Deedlit, Cosette, and Isabeau~*~