Why Is My Dog Losing Hair?

All dogs shed — some more than others, and most shed more during spring and fall as their coat transitions. This is normal and not hair "loss." True hair loss (alopecia) means thinning, bald patches, or failure to regrow hair after shedding.

Allergies are the most common cause of hair loss in dogs, because the associated itching leads to scratching, biting, and rubbing that breaks and removes hair. Flea allergy dermatitis is the single most common cause of hair loss — even a few flea bites can trigger intense itching and hair loss in allergic dogs, typically affecting the lower back, tail base, and inner thighs.

Hormonal (endocrine) disorders cause a characteristic pattern of symmetric hair loss without itching. Hypothyroidism causes bilateral hair loss along the flanks and trunk with a dull, dry coat. Cushing's disease causes similar symmetric hair loss with thin skin, pot belly, and increased thirst. Both are treatable with medication.

Skin infections (bacterial pyoderma or ringworm) create circular patches of hair loss, often with redness, scaling, or crusting. Ringworm, despite its name, is a fungal infection that's contagious to other pets and to humans.

Demodectic mange (Demodex mites) causes hair loss typically starting around the eyes and mouth in puppies. Sarcoptic mange (scabies) causes intense itching with hair loss and is contagious.