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What Causes Hair Loss in Dogs?

Alopecia, or hair loss, in dogs has a range of causes, from environment to genetics. Let's examine the four most common.

Melvin Peña  |  Apr 30th 2015


Male pattern baldness runs in my family, and has, over the last several years, begun to announce itself with increasing prominence. It’s a bit of a sore subject for me, and the Hippocratic wreath developing atop my head sounds more distinguished than it feels. Dogs are not as vain as humans, but hair loss in our canine companions can signal a variety of substantive health issues.

Pomeranian dog by Shutterstock

Since the vast majority of a dog’s body is covered in fur, hair loss in dogs can be an alarming sight for dog owners. Hair loss, both in humans and dogs, is evidence of a medical condition known broadly as alopecia. Let’s look at four of the most common reasons behind hair loss in dogs, some of which are more serious than others.

1. Shedding and genetics

Seasonal shedding is the most common reason for voluminous and sudden hair loss in dogs. There is a common misconception that the less hair a dog has to begin with, the less hair loss the dog will experience during fall and spring shedding seasons. It is believed that dogs who shed less are hypoallergenic. Dog allergies are caused not by hair itself, but by proteins present in the skin itself and in the saliva of dogs. For dog owners who have never experienced heavy seasonal shedding before, the sight of dog hair suddenly appearing all over the house can be alarming, but it is completely natural.

Dog scratching his face by Shutterstock

It may be unusual, but alopecia can also be genetic in otherwise healthy and fur-covered dogs. This condition, known as follicular dysplasia, has the same primary symptom as normal hair loss in humans. Hair follicles begin to shrink and hair either grows in thinner, or disappears, creating what we would call bald spots. This form of dog hair loss looks strange, but if the dog takes no notice, there may be no cause for concern.

2. Mange

If the dog is licking or scratching at these spots, however, the cause might be an infection or infestation. Mite infestations are a second cause of hair loss in dogs. There are two varieties of mange in dogs — demodetic and sarcoptic — of which demodetic is the most common. Though it may be horrifying to consider, most dogs live with a native population of mites on their bodies. Under normal circumstances, the number of these mites is held in check by a dog’s immune system.

What we refer to as mange is an affliction that occurs when the dog’s immune system is compromised or otherwise weakened, and the mite population begins to explode. Left unchecked, the excess mites cause dogs to itch, scratch, lick, and bite at spots on their body. Dog hair loss with mange is not due to the mites themselves, but to the wounds that the dog creates by the scratching and gnawing. These wounds create space for bacterial and fungal infections to take root, leading to hair loss.

3. Skin infections

Under the rubric of skin infections that cause a dog to lose hair, the most common is ringworm. Ringworm is not a worm, but rather a fungus that feeds on a dog’s skin and hair. Since fungi require moisture and heat to grow and spread, hair loss due to ringworm is frequently observed during the most humid parts of the year. If a dog’s hair loss is occurring on the extremities — her tail, forelegs, head, or on the top of her paws — the ringworm fungus might be the cause.

Dermatitis on dog by Shutterstock

You’ll recognize ringworm by its clearest symptom, the pinkish or reddish ring present in the patch of skin where the dog is losing hair. Ringworm fungal infections are self-limiting. In many instances, hair loss due to ringworm will stop within a few months. Dog owners should be more proactive, though, as ringworm is a zoonotic disorder and can be passed to humans. Topical antifungal medications, both over the counter and prescription, will expedite healing, hair recovery, and limit stress on you and your dog.

4. Stress and allergies

We all know what it feels like to be so stressed that we’re “pulling our hair out.” Dogs experience stress as well, and there are certain stressors that may cause a dog, literally, to lose hair. Separation anxiety takes a toll on dogs, especially when they are the only pet in the household. Ennui may cause a dog to lick, scratch, or bite at herself to pass the time. Repeated episodes can result in hair loss. Other common stressors that can lead to losing hair include unfamiliar social situations, air or car travel, extended periods of illness, and pregnancy.

Dog skin dermatitis by Shutterstock

People sometimes experience allergic reactions to dog dander and saliva, but dogs can have allergies as well. Dog allergies that cause hair loss vary widely, and include reactions to sudden dietary changes, medications, and exposure to household cleaning products. The most common source of allergic hair loss in dogs is a flea or tick bite. Like ringworm fungus, flea and tick infestations can happen at any time of year, but are frequently observed in the summer months.

Have you ever dealt with canine alopecia?

For most dog breeds, hair loss accompanied by itching, biting, or open wounds may signal any number of concerns. We’ve only covered the most common here. Alopecia is not always symptomatic of a health problem, however. There are certain dog breeds — the American Hairless Terrier, Chinese Crested, Peruvian Inca Orchid, and Xoloitzcuintle, specifically — for whom hairlessness is a simple fact of life and genetics.

Chinese Crested dog by Shutterstock

Chinese Crested dog by Shutterstock

Have you ever owned a dog who experienced a bout of hair loss? Were you and your veterinarian able to find that it was caused by genetic predisposition, a parasitic infestation, a bacterial or fungal infection, or stress? Was the hair loss due to a rarer condition? Share your experiences with and stories about canine alopecia in the comments!

Learn more about dog hair and skin on Dogster:

About the author: Melvin Peña trained as a scholar and teacher of 18th-century British literature before turning his research and writing skills to puppies and kittens. He enjoys making art, hiking, and concert-going, as well as dazzling crowds with operatic karaoke performances. He has a one-year-old female Bluetick Coonhound mix named Idris, and his online life is conveniently encapsulated here.