It sounds very much like your dog has contracted Ringworm, characterized by a reddish to brownish raised or bumpy patch of skin that may be lighter in the center, giving the appearance of a ring. Contrary to the name, ringworm is not in fact a worm but a fungal infection. the vast majority of cases in dogs are caused by Microsporum canis, Microsporum gypseum or Trichophyton mentagrophytes. The fungus thrives on skin that is moist, hot and hidden from the light and is therefore normally first found on the underside of dogs.

Ringworm can infect cats, dogs and humans and you can therefore contract it from your dog or from items which have been in contact with your dog. Most adult dogs have some resistance to ringworm and therefore do not develop any symptoms after coming in contact with infected animals or items. Your vet will need to take a sample of skin cells from around the infected area and create a cell culture to identify the infection. In most cases, small infections will heal on their own within a couple of months, but only if the infection did not take hold because of an underlying deficiency in your dog’s immune system. Your vet will be able to provide or recommend a topical anti-fungal treatment, anti-fungal shampoo or oral anti-fungal course.