If your dog has a moist, raw, painful, foul-smelling, pus-oozing circular sore, he may have a bacterial surface infection known as a hot spot. When the skin develops an inflammatory response to somethingpollen allergies, flea bites, moisture trapped beneath a matted or unshed coatfollowed by an overgrowth of bacteria on the area, a hot spot forms.

Developing on the neck, ears, chest, back, rump, and flanks, hot spots progress through self-mutilation. Hot spots occur when an area of the skin becomes acutely itchy, so the dog chews at it, says Linda A. Frank, DVM, diplomate of the American College of Veterinary Dermatologists and a dermatology professor at the University of Tennessee. It then becomes moist and subsequently more itchy, leading to a vicious cycle.

Within hours, hot spots can enlarge to several inches in size. To treat, Frank says, remove the surface bacteria by clipping away the hair to let in air and by cleaning the spot one to two times a day with an antibacterial or anti-itch shampoo. [Follow this with] a drying agent that has menthol in it or something with a topical anesthetic such as pramoxine or lidocaine. Don't use an alcohol-based product as that will really burn. An itch-decreasing medication such as predisone may be prescribed by your veterinarian if the itching is intense. This is usually enough to break the itchy cycle and allow healing. 

If you don't see healing of the hot spot with no more itching within two or three days, your veterinarian should examine your dog. In most cases, the hot spot remains just a surface infection, although occasionally a dog will have a deeper infection, which may require antibiotics.

You can reduce the risk of hot spots, Frank says, by using an effective flea-control program and grooming your dog's coat regularly.