Inc. Veterinary Services Department Description and cause Also known as acute moist dermatitis, hot spots are usually a disease of dogs with long hair or those with dense undercoats. It is often caused by a local allergic reaction to a specific antigen. Insect bites, especially from fleas, are often found to be the cause. Hot spots are circular lesions, usually found on the head, over the hip and along the side of the chest. They will be moist, raw, inflamed and hairless, and can be quite painful.
Animals usually lick, bite or scratch the area, and thus irritate the inflamed skin even more.
Hot Spots can change dramatically in size in a very brief period of time. What was the size of a quarter may easily be eight inches in diameter in six hours. The lesions are rare in the colder temperatures of winter. They occur in equal frequency in both inside and outside dogs. Many dogs develop several of these lesions over the course of their lives.