Identifying Skin Diseases in Dogs

Allergic contact dermatitis: Same as contact dermatitis, but rash may spread beyond area of contact. Requires repeated or continuous exposure to allergen (such as wearing a flea collar).

Canine atopy: Severe itching that occurs in young dogs and begins in late summer and fall. Caused by seasonal pollens. Occurs in mixed breeds as well as purebreds.Common.

Chiggers: Itching and severe skin irritation between toes, and around the ears and mouth. Look for barely visible red, yellow or orange chiggers.

Contact dermatitis: Red, itchy bumps and inflamed skin at the site of contact with chemical, detergent, paint or other irritant. Affects feet and hairless parts of the body.

Damp hay itch (Pelodera): Red pimplelike bumps on skin. Severe itching. Occurs in dogs bedded on damp hay and similar grass.

Flea allergy dermatitis: Red, itchy pimplelike bumps over the base of the tail, back of rear legs and inner thighs. Scratching continues after fleas have been killed.

Fleas: Itching and scratching along the back, around the tail and hindquarters. Look for fleas, or black and white gritty specks in hair (flea feces and eggs).

Fly-bite dermatitis: Painful bites at tips of erect ears and bent surfaces of floppy ears. Bites become scabbed, crusty-black and bleed easily.

Grubs: Inch-long fly larvae that form cystlike lumps beneath the skin with a hole in the center for the insect to breathe. Often found beneath chin or along abdomen.

Lice: Two-millimeter-long insects, or white grains of "sand" (nits) attached to hair. Not common. Found in dogs with matted coats. May have bare spots where hair has been rubbed off.

Lick granuloma (acral pruritic dermatitis): Red, shiny skin ulcer caused by continuous licking at wrist or ankle. Usually seen occuring in large, short-coated breeds.

Maggots: Soft-bodied, legless fly larvae found in damp matted fur.

Scabies (Sarcoptic mange): Intense itching. Small red spots that look like insect bites on the skin of the ears, elbows and hocks. Typical crusty ear tips.

Ticks: Large insects attached to skin. May swell up to size of pea. Found beneath ear flaps and where hair is thin.

Walking dandruff (Cheyletiella mange): Occurs in puppies 2 to 12 weeks of age. Large amounts of dry, scaly, flaky skin over the neck and back. Itching is variable.

Source: http://www.nzymes.com/articles/dog_skin_hair_problems.htm