Hair loss in dogs goes by a single clinical name — alopecia — but the causes behind it range from a flea allergy you can treat at home to a hormonal condition that requires lifelong management. The bald patch itself tells you very little. The context around it tells you almost everything.
The first question: is your dog scratching?
Vets organize alopecia diagnostically around one key feature: whether or not it itches. This distinction narrows the cause list dramatically.
Pruritic alopecia — hair loss with itching — usually means the dog is creating the bald patch themselves. Scratching, chewing, or rubbing at itchy skin removes the hair mechanically. The underlying cause is almost always parasites (fleas, mites, lice), a skin infection (bacterial or yeast), or an allergy. These causes tend to respond well to treatment: remove the trigger, treat the secondary infection if one has developed, and the hair comes back.
Non-pruritic alopecia — hair loss without obvious discomfort — is trickier. The dog often doesn’t notice it, and neither does the owner until the patch is already substantial. These cases tend to involve hair follicle abnormalities, hormonal imbalances (hypothyroidism and Cushing’s disease are the two most common), or disruptions in the normal hair growth cycle. A skin biopsy reviewed by a veterinary pathologist may be necessary for a definitive diagnosis.
Common causes
Parasites produce itchy, patchy hair loss that often follows predictable patterns — around the tail base with fleas, on the face and ears with mange mites. The key is that treatment of the parasite resolves the hair loss; ongoing baldness after treatment suggests there’s something else going on.
Allergies — environmental or food-related — cause chronic skin inflammation that leads to self-trauma and hair loss over time. The distribution is usually bilateral and symmetric, affecting the paws, belly, and face more than the back.
Hormonal conditions typically produce non-itchy, symmetric hair loss that starts at the trunk and spares the head and limbs. Hypothyroidism adds a dull, brittle coat and weight gain. Cushing’s disease produces a pot-bellied appearance alongside the hair loss and causes increased thirst and urination.
Ringworm (a fungal infection, despite the name) causes circular patches of hair loss with a scaly border. It’s contagious to humans and other pets, so diagnosis and treatment are time-sensitive.
Genetic alopecia is an expected feature in certain breeds. Xoloitzcuintlis, Chinese Crested dogs, American Hairless Terriers, and Peruvian Inca Orchids are all bred for hairlessness — baldness in these dogs isn’t pathological, it’s the point. But even these breeds come in coated varieties, which can develop alopecia from the same causes as any other dog.
Other signs to watch alongside hair loss
Alopecia rarely presents in isolation. Pay attention to changes in skin color (darkening or lightening), crusting or scaling, discharge, inflammation, or open wounds at the bald site. Any of these point toward a diagnosis that needs veterinary workup rather than a wait-and-see approach.
When to see a vet
Any bald patch that’s growing, accompanied by skin changes, or affecting your dog’s comfort level warrants a veterinary appointment. Bring notes on when you first noticed it, whether it seems to itch, and any recent changes in diet, environment, or routine. That history takes your vet significantly further toward a diagnosis than the patch alone.
The treatment path depends entirely on the cause. Some cases of alopecia resolve fully; others are managed rather than cured. The earlier the diagnosis, the more options remain on the table.
