TL;DR: Circular hair loss in dogs is typically caused by common conditions like ringworm or skin infections and is rarely an emergency unless the skin is bleeding, oozing, or causing extreme discomfort.
What causes circular hair loss in dogs?
Finding circular patches of missing fur on your dog can be concerning, but please know that this is a very common issue that veterinarians see regularly. These distinct, coin-sized spots are often caused by ringworm (a fungal infection), bacterial skin infections, or even mites. While it can look uncomfortable, it is usually a localized skin condition rather than a sign of a life-threatening illness.
Is circular hair loss in dogs an emergency?
- Urgency Level: Low. In the vast majority of cases, circular hair loss is not an emergency.
- If your dog is otherwise acting like themselves—eating well, staying active, and not in visible distress—you can typically wait for the next available appointment with your primary veterinarian.
- Seek care sooner if the area is oozing, bleeding, or if your dog is scratching so intensely that they are causing self-injury to provide them with relief.
How does taking a photo help diagnose my dog's hair loss?
- A clear, high-resolution photo allows a veterinary professional to see the exact color, texture, and borders of the hair loss.
- A quality image helps us differentiate between a simple dry patch and something more infectious like ringworm.
- Taking a photo today gives you a baseline to track whether the patches are growing or spreading while you wait for your appointment.
Clinical Context (Merck Veterinary Manual)
Focal areas of alopecia, 0.5-2 cm in diameter, can develop from easily epilated hairs. Mild epidermal collarette formation may be present at the margins of hair loss, but follicular pustules and erythema are often absent, particularly in shorthaired breeds. In Collies and Shetland Sheepdogs, widespread alopecia with mild erythema and epidermal collarette formation at the expanding edge can mimic endocrinopathy. Pattern baldness affecting the pinna has been reported in Dachshunds, Chihuahuas, Italian Greyhounds, and Whippets with suspected hereditary predisposition, beginning as thinning hair that may progress to complete pinnal alopecia.
Chapter: Dermatology
Source: The Merck Veterinary Manual, 11th Edition (Page 842)