Scratching

If your pet spends a large portion of its time scratching or licking himself or herself too much they may have pruritus, or itching. Itching is caused by chemical reactions in your pet’s skin. Usually this is caused by allergies or parasitic skin disease. Allergic Skin Diseases

Flea allergy is the most common allergic skin disease in the United States. Dogs with flea allergy tend to scratch their back ends leading to lesions on the rump, hind legs, tail and belly. Since it takes just one flea to make the dog react, the presence of fleas on the dog may be minimal to absent.
Atopy is a reaction to airborne allergens such as pollens, house dust, house dust mites and molds. Dogs with atopy tend to scratch their ears and face and tend to chew and lick at their feet. The condition is often worse during summer months when pollen and mold levels are increased.
Helpful products: Allerase spray, Allerpet C, Allerpet D.
Food allergy is a reaction to one or more ingredients in their food. These dogs tend to scratch in the same places as those with atopy.
Insect allergies (insect bite hypersensitivity) are one of the most common allergies. Lesions are evident in areas where insects such as bees are likely to bite (bridge of nose, ears).
Contact allergy is a reaction to an irritant that touches the skin, often the belly or chest. Allergies of this type are rare.

Parasitic Skin Diseases

Scabies is an intensely pruritic skin condition caused by the sarcoptic mange mite. Lesions are seen on the ears, elbows and hocks (ankles).
Demodectic mange is caused by the demodex mite. This is usually a disease of young dogs and causes dramatic hair loss and dermatitis. This disease is often not pruritic, but can lead to a secondary bacterial infection of the skin (pyoderma), which may be itchy.
Fleas can cause pruritus in dogs that are not flea allergic, although the degree of pruritus is less severe.
Cheyletiellosis is an itchy skin condition caused by the cheyletiella mite. Lesions are usually most dramatic along the top of the back. These mites are sometimes visible to the naked eye as small, moving, white specks, hence the name "walking dandruff mite".
Ear mites cause itching of the ears in dogs and can sometimes cause itching elsewhere on the body.
Lice are small insects that are easily seen with the naked eye that can cause pruritus.