dermatitis?

Today I noticed a spot on my cats neck maybe half an inch in diameter where there is a red/dry spot and no fur. After doing some research online I'm beginning to think its dermatitis. Anyone have any suggestions when it comes to treating this, and what shampoos to use?

Thx in advance.

Is that the only symptom ?  Are there any acne type bumps anywhere ? 

The reason I ask is because my ould girl Checkers is horribly allergic to fleas. If she gets one flea she breaks out in bumps. if not treated they will turn in to red hot spots. She is an indoor kitty so it doesn't happen very often, but when it does we treat her with Advantage immediately. Her skin clears up quickly once she is treated.