Pursuing the Causes of Hair Loss

Allergic dermatitis is the most common culprit

by Debra M. Eldredge, DVM

With the exception of those bred for hairlessness like the Chinese Crested, dogs should have a full coat of hair. Whether it's a short, tight coat, a thick undercoat that sheds in the spring or long, coarse hair that guards soft under fur, when it begins to fall out, you'll have to do some detective work. That's because the causes can range from external parasites to hormonal conditions to allergies, genetics and behavior problems.

Leading the list is flea-allergic dermatitis. It's the most common cause of hair loss seen by Michael Stone, DVM, a specialist in internal medicine at the Cummings School of Veterinary Medicine at Tufts University. "Fleas bite your dog and cause scratching from irritation, but many dogs also experience flea allergy," he said. "Those dogs will itch from the allergic reaction to the saliva of even one flea bite."
Dogs with flea problems will usually have red skin and severe inflammation. You can see the fleas by pulling the hair back or rolling your dog over and looking at the groin area. Fleas in the rump area may be more difficult to see, but one telltale sign is black specks. They're dried flecks of blood excreted by adult fleas.

Many dogs will show signs of secondary bacterial infections and may require antibiotics, other medications to ease the inflammation and itching, and possibly topical treatments to kill the fleas. Treating a flea infestation means killing the adult fleas as well as the larvae in your house.

Other external parasites include mites - both the itchy sarcoptic mange mite and the ubiquitous demodectic, or red mange mite. Sarcoptic mange mites make dogs miserable. They'll itch almost incessantly. Veterinarians diagnose mites using skin scrapes. They'll prescribe topical treatments, supportive care and sometimes antibiotics.

Demodectic mites, present on many dogs, result in few problems, but when an overgrowth occurs in the hair follicles, patchy hair loss develops. "While demodicosis is not usually itchy, if a secondary bacterial infection develops, itching may occur," Dr. Stone said.
If you find a parasite on your dog, save it to show your veterinarian - and wait to bathe your dog until after his appointment. Important diagnostic information may be lost in the bath.

While people with allergies tend to sneeze and wheeze, dogs often show skin problems, including hair loss secondary to inflammation and itching. Culprits may he allergens in the air your dog breathes, his food or substances that get on the skin. Your veterinarian will work with you to determine the offending substances and develop a plan to avoid them, and reduce reactions with medications or desensitization.

Some breeds have a genetic predisposition to hair loss. This may show up in certain color variants, such as the fawn or blue Doberman Pinschers. The condition is called color dilution alopecia. The dogs aren't usually itchy, but their haircoats become thin.
Breeds with thick, heavy coats are prone to hotspots. They'll have inflamed areas without protective hair. The spots tend to occur in hot, humid weather.

Sebaceous adenitis is an inflammatory skin condition leading to abnormal hair growth and/or hair loss. Poodles and Akitas are known to suffer from it. A skin biopsy diagnoses the condition.

With any luck, however, your dog's hair loss may simply he seasonal shedding, and his coat will be hack to its full glory in a short time.

Debra M. EIdredge DVM, is in private practice in New Hartford, N.Y.

Hormonal and Behavior Problems Can Also Cause Shedding

Dogs with thyroid problems can show a wide of symptoms, but often owners first notice a thinning of the haircoat. The dogs aren't usually itchy, and their skin may appear normal, even though they have significant hair loss. Cushing's disease, or hyperadrenocorticism, can also cause hair loss. Blood tests can identify both disorders.

Dogs with sepration anxiety and other behavior problems may lick or chew at themselves causing hair loss and deep sores. Some breeds, such as Doberman Pinschers, show a genetic predisposition to the condition, including flank sucking. Behavior altering drugs, combined with behavior modification techniques, may be needed to help stop this type of hair loss.