3. Mange and Other Parasites

Mange is a catch-all term for itchy skin infections caused by mites. Mites are microscopic creatures that live on the surface of the skin or in hair follicles. They cause hair loss and itching by burrowing or chewing on skin. Some mites, like the scabies mite, are extremely contagious to both humans and other dogs, notes the Merck Veterinary Manual. Other mites, like demodex mites, aren't contagious but still cause hair loss and may require treatment.

Fleas are a very common reason for a dog losing hair. Fleas can make dogs itchy to the point of scratching their hair off. The location of hair loss can be a good clue, as fleas tend to most often cause scratching around the head, neck, and base of the tail.

Fleas and some mites are extremely contagious, so any parasites you find on your dog may have already spread to your home and other pets. If you find evidence of mites or fleas, your veterinarian can prescribe an antiparasitic treatment and offer tips for ridding your house of pests. Remember, most mites are not visible with the naked eye and fleas spend most of their time in your soft furnishings, so just because you haven’t seen parasites, that doesn’t mean they can’t be causing your dog’s hair loss. 

4. Allergies

Dogs can develop allergies just like humans, and some of the most common signs are itchy skin and hair loss. The most common allergies in dogs are:

• Environmental allergies (atopic dermatitis or atopy) to irritants like pollen, mould and dust mites

• Flea allergies

• Food allergies

If your veterinarian suspects allergies, they may recommend flea control, medication to control the itching, avoiding allergens, or a food trial to rule out food allergies.

Food allergies can only be diagnosed by running a food trial for a minimum of 10-12 weeks. If your veterinarian puts your dog on a food trial with a limited-ingredient meal plan or therapeutic food, it is critical to make sure your dog does not eat anything else while on the trial. One treat or stolen bite of chicken can confound the results. If the underlying cause is allergies and they are treated properly, your dog's hair should regrow and the itching should stop.

5. Underlying Medical Conditions

If a dog is losing hair all over their body, or in specific places, especially if they are not itchy, then there may be an underlying medical condition. The skin is the largest organ in the body, and it requires tremendous amounts of nutrients and functioning body processes to stay healthy. If your dog has an underlying medical condition, skin and hair changes may be the first sign of problems.

Hormonal conditions, like hypothyroidism, adrenal gland disorders or growth hormone disorders, can all cause a dog to lose hair. If your veterinarian suspects an internal problem as the cause of the hair loss, they may recommend laboratory testing and possibly X-rays or ultrasound imaging to determine the cause.

Excessive shedding can also be caused by stress, poor nutrition, pregnancy or lactation. If you think your dog is shedding more than normal, or if they’re developing bald patches, schedule an appointment with your veterinarian. The treatment they prescribe will depend on your pet's diagnosis and their other health needs.

A dog losing hair needs to visit the veterinarian, but their condition can often be cleared up with a simple change in food or medication. It can take time to get to the bottom of hair loss as there are so many possible causes, so work with your vet and try to be patient as they rule things in or out. Keeping up with regular grooming and brushing, and knowing what’s normal for your dog, will help you spot the earliest signs of a problem.