Primer On Ringworm

Written and reviewed by John A. Bukowski, DVM, MPH, PhD
and Susan E. Aiello, DVM, ELS

Despite its name, ringworm (also known as dermatophytosis)  is caused by fungus, not by worms. 

Fungi known as dermatophytes can infect your dog's hair and dead skin, leading to bald, scaly areas with broken hairs. These areas can show up simply as patches, or as rings.

Ringworm shows up most often on the feet, face, ears, and tail. 

The infection is usually confined to hair, nails, and dead skin, but inflammation and redness of other parts of the skin can develop from the body's immune response to the fungus.

This inflammation can cause your dog to itch and scratch, and a secondary bacterial infection may develop.

Ringworm is infectious and can be passed to other animals or to people in the household.

Ringworm can be diagnosed in a variety of ways.

Some of these fungal organisms will fluoresce under ultraviolet light, so your veterinarian may be able to make the diagnosis during your dog's visit by examining its hair and skin under a special light.

In some cases, your veterinarian may recommend a fungal culture, in which a sample of your dog's hair and skin cells are placed on a special medium in an attempt to grow the fungus for both diagnosis and identification. Cultures can take several days to a couple of weeks. Sometimes, fungal material can also be seen directly under the microscope.

Ringworm can clear up on its own, but treatment speeds recovery and helps prevent the condition from being passed to other animals (and people) in the household. 

Repeated bathing with a medicated shampoo removes dead hair and skin and inhibits fungal development.

Oral medications are also available, and usually need to be continued for weeks to months. All pets in the household may need to be treated, because some animals can carry ringworm without showing any signs of infection.

Pet bedding, brushes, and other household items in contact with your dog may need to be cleaned or discarded.


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  1. Wow, this is good information. I never knew ringworm was caused by a fungus. It's one of the conditions the shelter staff where I volunteer talked with us about - the potential of picking it up from a shelter dog and bringing it to our own dogs. I always clean up really well but it's something I get a little worried about. Is that a genuine concern? Thanks for this post!


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