If your dog spends a large portion of his time scratching, he may have a condition known as pruritus, or itching, an unpleasant sensation that causes your dog to scratch or bite at himself. It is caused by chemical reactions that occur in the skin and stimulate the nerves, causing the brain to feel the itch. In fact, the act of scratching itself may stimulate these inflammatory reactions in the skin and make the condition worse. Any skin condition that causes inflammation can cause pruritus.
How pruritis affects your dog's health depends on the degree of the pruritus. Mild pruritus may hardly have any effect at all. However, severe pruritis leads to intense scratching, which may result in painful skin lesions that may become infected. Your dog will often whimper or cry out and may have trouble sleeping.
Every dog has a threshold of pruritis or an "itch threshold." This is the point where all of the sources of itching finally add up to enough irritation to cause the irresistible urge to scratch. Scratching begins when the stimulation exceeds that threshold. For example, a dog with a mild allergy to house dust mites may be below the threshold but may begin to scratch severely when he becomes infested with fleas.
Pruritus is associated with other skin diseases, including secondary bacterial skin infections (pyoderma) and secondary yeast infections. But it is the main symptom of skin conditions like allergies and skin parasites.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.
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 less common than other 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.
Acute moist dermatitis, also known as hot spots, are localized, moist, reddened bacterial infections of the skin. These can be very itchy, causing the dog to lick or chew the area. This further damages the skin, and creates a cycle of itching, scratching and chewing.
Pyoderma is an infection of the skin that can be quite pruritic. Pyoderma can be superficial or deep and is often secondary to another skin disease.
Ear infection, otitis, can cause significant itching of the head. Affected dogs will shake their heads and scratch at their ears.
What To Watch For
Scratching or biting. If this continues beyond one day and leads to lesions such as hair loss, reddening of the skin and obvious pain or discomfort, have your dog evaluated by your veterinarian.
Chronic licking of the feet. This is also a symptom of pruritus.
The key to treating pruritis is to identify and treat the underlying cause. Your veterinarian may want to perform some diagnostic tests to determine the cause. The condition may be relieved with medication but the itching often recurs after the medication is finished.
At Home Care
At home your care will be aimed at preventing pruritis by keeping your dog's coat clean and brushed free of mats. Consult with your veterinarian to establish a complete flea control program. If your dog is being treated for pruritis, administer all prescribed medication and follow all your veterinarian's instructions.