You may want to have your vet take a quick look. An exam is cheap. Could just be fly eaten (can get something like flys off at a pet shop usually to keep the away), or something like a bacterial or fungal infection and is also a sign of sarcoptic mange. A few of those may be contagious to people under the right circumstances and you would to get your pup safely and effectively treated.
www.marvistavet.com
www.marvistavet.com