Thought this was very interesting & full of 411 (info):
Skin Problems in Dogs Slideshow: Mange, Allergic Dermatitis, Impetigo, Ringworm, More
If in any doubt, get your dog to a vet & have a skin scrape w/cytology done. They collect the affected skin gently & look under the microscope to determine if it's parasitic, fungal, bacterial, even cancer! Cytology will determine if the tissue is inflammatory, an infection & will confirm if a dog has mange. It is not an expensive test!
http://www.vcaspecialtyvets.com/ckfi...%2520final.pdf