Why Is My Dog Losing Hair in Chunks?

Once or twice annually, depending on coat type, your dog will shed her fur in chunks. The intense shedding is most obvious in dogs with double coats consisting of a soft, insulating undercoat and a harsher, weatherproof top coat. Cyclical hormonal changes cause unspayed females to lose their coats. In both males and females, seasonal changes spur coat changes. Some dog owners call this shedding "blowing the coat" or "molting." The heaviest fur loss typically continues for two weeks. Brush your dog frequently to keep her comfortable and your home fur-free.

Mange causes hair loss in patches rather than chunks. There are two common types of mange: demodectic and sarcoptic.

Dogs generally carry some demodex mites in their hair folicles. Normally demodex mites are harmless, but a temporary or chronic immune system deficit can allow them to increase in number, causing inflammation and bald patches. This sometimes occurs in a minor way briefly at puberty, when you may notice a small patch or two of demodectic mange on your young dog's face. This generally clears up without treatment, but you should consult your veterinarian if you see it.
Hair loss in patches over your dog's body caused by demodex mites means some issue has compromised the dog's immune system, allowing the mites to multiply. It is important to seek veterinary care. Demodectic mange generally is not communicated to other dogs or people, but it is a serious health issue for your dog.

Unlike demodectic mange, sarcoptic mange is highly contagious. It also is highly treatable. Your dog can catch the Sarcoptes scabei skin mite from other dogs, and you can catch it too. Signs in your dog are frantic scratching and restlessness. Symptoms appear about one week after infection. Your dog is likely to have hair loss, red skin, sores and scabs. Quick action is needed to protect both your dog and you. Your vet will probably advise isolation of the dog, combined with anti-parasitic and anti-itch medications. You can expect the problem to clear up in about a month.

Dogs, like humans, can have atopic dermatitis and eczema due to allergy. These can lead to your dog developing bald patches. Some breeds seem more susceptible to such skin problems, but dogs of any breed can have them. Hair loss may be caused by flea allergy or to an allergy to any of a wide variety of substances, ranging from antibiotics and food additives to wool or nylon fabrics and household deodorizers. Some dogs may also develop acral lick dermatitis (ALD), also called lick granuloma, in which the dog licks himself excessively in one spot, creating a hard-to-heal wound, surrounded by thickened skin. Often the root cause of this behavior is psychological, the dog's reaction to stress, anxiety or boredom.