What Causes a Circle of Hair Loss on My Older Dog’s Neck?

A single round patch of hair loss with scaly edges and no itching has several possible causes. Ringworm, a fungal infection, often looks just like this, and it's contagious to other pets and people, so it's worth checking first. Other possibilities include a bacterial skin infection, a reaction at a vaccine or injection site on the neck, and demodectic mange, which in an older dog can be a sign of another health problem.

Sarcoptic mange is less likely, since it's usually intensely itchy and tends to start on the ear edges, elbows and belly.

Have your vet take a look. They may do a skin scraping for mites and a fungal culture or other test for ringworm. Until you know what it is, wash your hands after touching the spot, avoid sharing bedding, and keep an eye on your other dog for any new patches. Read more about ringworm on dogs and how it's diagnosed.

This is general information, not a diagnosis. Please follow your own vet's advice.