Hot spots (also called acute moist dermatitis or pyotraumatic dermatitis) are localized, moist, reddened areas on the skin caused by self-mutilation. Acute moist dermatitis is a very common skin disease of dogs. hot spots are frequently seen in long-haired and heavy-coated breeds, and are more prevalent during the summer months.

The precise sequence of events leading to acute moist dermatitis is not known but anything that can initiate an itch-scratch cycle can lead to acute moist dermatitis. Common underlying causes of hot spots include allergies (flea allergy, atopy, food allergy), parasitic diseases (sarcoptic and demodectic mange), anal gland disease, clipping and grooming. Less common causes of hot spots include ringworm (dermatophytosis), drug reactions, autoimmune disease in which the body fails to identify self-components and reacts against normal tissues, and vasculitis (inflammation of blood vessels).

Clinically, the lesions of acute moist dermatitis are secondary to self-inflicted trauma. Strangely, even severe self-trauma in some dogs will not create a hot spot while in others minimal self trauma may do so.

The role of bacteria in the development of hot spots also is not clear. Some cases of acute moist dermatitis seem to be initiated by folliculitis (i.e. inflammation and infection of hair follicles), and this seems to be common in Saint Bernards and Golden retrievers. Other affected dogs do not seem to have an important bacterial component and respond to clipping of the hair, cleansing of the skin and corticosteroid therapy.

Related Symptoms or Ailments

The lesions of acute moist dermatitis are reddened (erythematous), swollen, and hairless. They exude a serous discharge and are painful. Their onset and progression are rapid. Pruritus (itchiness) is intense, and severe self-trauma can cause severe lesions in a very short period of time.

Two types of acute moist dermatitis occur. One type does not have an important bacterial component and manifests as a superficial ulcerated plaque. The second type, in addition to being an ulcerated plaque, also has peripheral papules (small reddened bumps) suggestive of bacterial folliculitis.

Typical locations of hot spots are the hindquarters and the sides of the face below the ear. Lesions on the hindquarters usually are caused by underlying flea allergy, whereas those on the side of the face usually are associated with concurrent ear inflammation (otitis) secondary to allergies.