Bacterial Skin Infections (Pyodermas)

Staphylococci bacteria are the most common organisms found in bacterial skin diseases in dogs. These bacteria (S. intermedius) are not contagious to humans or other pets. Commonly itchy, yellow pustules are observed early in the disease, and the dog’s skin can be reddened and ulcerated. Dry, crusted areas appear as the condition advances, along with hair loss and foul odour.

Fungal Skin Infections (Ringworm)

The fungal skin infections of dogs are caused primarily be two species of fungi: Microsporum and Trichophyton. The skin diseases resulting from these fungi are commonly called ‘ringworm.’ Ringworm is seen most commonly in young animals. The fungi live in dead skin tissues, hairs and nails. Hair loss, usually in circular patches, may appear. If infected, the center of the patches may have a dry, crusty appearance. The head and legs are most commonly affected by ringworm, although the disease can spread over other parts of the dog’s body if not treated. Ringworm is contagious to humans and to other household pets. After treatment begins a cure can take as long as 2-3 months or more.

Parasitic Skin Diseases

Fleas are the most common parasitic skin disease found in dogs. Mange is another type of skin disease which is caused by mites. There are two severe types of mange: sarcoptic mange and demodectic mange. Sarcoptic mange causes intense itching, hair loss and crusting of the skin. A dog’s ears, front legs, chest and abdomen are most often affected by sarcoptic mange.

Demodectic mange can cause itching. The skin is reddened and scaly, and hair loss occurs in round patches resembling ‘ringworm.’ The face and front legs are most commonly affected, although some cases may be generalized. Generalized demodectic mange is often a sign of underlying internal disease or a hereditary problem. Ear mites, lice, and ticks are other parasites that affect dogs. Ear mites cause severe irritation in the ears. Often, an affected dog will scratch the hair off the back of its ears. Ticks, lice and fleas can transmit other diseases, in addition to causing irritation.

Hormonal Skin Diseases

Skin diseases caused by hormonal abnormalities in dogs are difficult to diagnose. The thyroid gland, adrenal glands, pituitary gland, testicles and ovaries all produce hormones. If excessive (‘hyper’) or deficient (‘hypo’), these hormones produce changes in the skin and hair coat. Most hormonal problems that affect the skin produce hair loss that is evenly distributed on each side of the dog’s body. The skin may be thicker or thinner than normal, and there may be changes in the color of the skin or hair coat. These diseases usually are not itchy. When any of the hormone-producing glands malfunction, they affect other body functions besides the skin. Hormonal skin diseases in dogs can be much more serious than a ‘skin problem.’ Some causes of hormonal skin disease, such as hypothyroidism and adrenal gland problems, can be diagnosed by special blood tests and effectively treated. Others may be more difficult to diagnose and treat. Skin changes related to the sex hormones can be successfully treated with surgical neutering, if this has not been performed previously.

Allergic Skin Diseases

An allergy is a hypersensitivity reaction to allergy-causing substances known as ‘allergens’ or ‘antigens.’ Dogs (like people) can develop allergies at any age, and the signs can appear quite suddenly. Signs such as itchy skin, nasal and eye discharges and sneezing, and/or digestive upsets and/or skin lesions may indicate an allergy is present.

Atopy (atopic dermatitis, allergic inhalant dermatitis) is a pruritic (itchy) skin disease dogs develop in response to inhaled particles such as house dust, molds and pollens. This common form of allergy usually starts at a relatively young age. Rarely, dogs can be allergic to chemicals contained in soaps, waxes, carpets and flea collars. This type of hypersensitivity is known as a ‘contact allergy.’ Also, some dogs are allergic to insect bites and stings. Itching is the primary sign of allergic skin diseases in dogs. The affected skin may appear normal, or red and moist in patches called ‘hot spots.’ Pus and dried crusts are apparent if a bacterial infection is also present. The dog tends to constantly scratch and lick affected areas. The most common allergy dogs develop is to flea saliva. The presence of a single flea on these allergic dogs causes intense itching. Initially, flea allergies are most evident over the dog’s back and near the tail. A dog’s face, feet, chest, and abdomen are more often affected by pollen and dust-type allergies. Contact allergies are seen mostly on the hairless areas of the abdomen and on the bottoms of the feet.