This could be mange mites or ringworm fungus or flea bite dermatitis.
Ringworm is potentially contagious to humans and you can read about it here
www.marvistavet.com/html/body_ringworm.html
There are two kinds of mange problems one is a contagious one that the dog can get from other dogs. You can read about sarcoptic mange here
www.marvistavet.com/html/sarcoptic_mange.html
One is an autoimmune disease problem called demodectic mange often shortened to demodex and you can read about that here
www.marvistavet.com/html/body_demodectic_mange.html
Skin infections from staph or other bacterial can look like this too.
All these things need vet treatment to resolve.
Hope this helps you!
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