Ringworm in Dogs: Symptoms, Contagion Risk & Treatment

Ringworm in dogs is not caused by a worm at all. It’s a fungal skin infection that produces round, bald patches with scaly or crusty skin, and despite the name, the patches aren’t always ring shaped. The reassuring part first: with a proper vet diagnosis and the right antifungal treatment, most dogs recover fully.

The part owners need to take seriously is that ringworm is zoonotic, meaning it can spread from your dog to you, especially to children, older family members and anyone with a weakened immune system. Treating your dog is only half the job. You also need to clean the house properly, because the fungal spores can survive in carpets, bedding and grooming kit for a long time.

What is ringworm, and why isn’t it a worm?

Ringworm gets its name from the ring shaped, red mark it causes on human skin, not because a worm is involved anywhere. Blue Cross describes it plainly: it isn’t a worm but a fungus, similar to athlete’s foot. The infection is caused by a group of fungi called dermatophytes, and in dogs the patches are often grey and scaly rather than a neat red ring, which is why it’s easy to mistake for other skin problems.

The fungus produces tough spores that survive being trodden into carpets, bedding and grooming kit. It only takes one spore landing on broken or damaged skin, a scratch, a graze, or an already irritated patch, to start an infection. A dog with healthy, unbroken skin is unlikely to pick it up even after contact with the fungus.

What does ringworm look like on a dog?

The classic sign is a roughly circular patch of hair loss. As the patch grows, the middle often starts to heal and regrow hair while the ring at the edge stays inflamed, which is where the name comes from in the first place. VCA vets describe the affected hair as fragile and easily broken, and note that the patches usually aren’t itchy, though they can sometimes become scabby. Patches most often turn up on the paws, legs, head and ears, though they can appear anywhere on the body, and occasionally the claws become rough and brittle too.

If your dog’s crusting is concentrated on the paw pads and nose rather than spreading as patches, it’s worth reading about crusty paws and noses in dogs as well, since hyperkeratosis can look similar at a glance but is a completely different condition.

Some dogs carry the fungus in their coat without ever developing visible patches. That’s one reason your vet may want to check any other pets in the house even if they look completely healthy.

Is ringworm contagious to people and other pets?

Yes. Ringworm spreads through direct contact with an infected animal, or by touching something the fungus has landed on: bedding, brushes, food bowls, furniture, even carpet.

Ringworm can be passed from your dog to you and other people who come into contact with your dog.

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In people, it usually causes one or two red, scaly patches and generally responds well to treatment, but VCA’s vets warn it’s more likely to take hold in someone with a weakened immune system. Blue Cross advises wearing gloves and an apron when treating an infected dog, and keeping children away from them until the infection has cleared. Puppies, senior dogs, and any dog that’s already unwell are most at risk of a serious infection too, so don’t sit and wait it out if your dog falls into one of those groups.

How do vets diagnose ringworm?

Because plenty of other skin conditions look similar, getting a proper diagnosis matters, and vets usually combine more than one check rather than relying on just one test.

Your vet may start by examining your dog’s coat under a Wood’s lamp, a UV light used in a darkened room. Merck’s vets note that 91 to 100% of untreated dogs infected with Microsporum canis, one of the fungi that causes ringworm, will glow under this light, but not every fungal species fluoresces, so a clear glow isn’t the end of the story.

The most reliable test is a fungal culture: your vet takes a sample of hair and skin and grows it in a lab to see what develops. VCA calls this the most accurate way to diagnose ringworm, though it can take from a couple of days up to three weeks for a result. PCR testing, which looks for fungal DNA, is faster, but VCA’s vets caution it can give false positives and doesn’t always identify which species is involved, which matters for judging how easily it could spread to people.

How is ringworm in dogs treated?

Most dogs need a combination of topical and oral treatment rather than one or the other. Your vet may clip the hair around affected patches, or your dog’s whole coat if the infection is widespread, to stop the fungus spreading further and let medicated shampoo reach the skin properly.

PDSA describes a typical plan as antifungal medicated shampoo used once or twice a week alongside a daily antifungal tablet, often for a month or more. VCA’s vets add that topical treatment alone can take several weeks to months, and oral treatment usually runs for a minimum of six weeks, sometimes longer, and they warn against stopping early even once the patches look better, because the infection can come back if it isn’t fully cleared.

If there are other pets at home, your vet will advise whether to treat just the affected animal or everyone in the household, depending on exposure and how easily that particular fungus spreads. Ringworm sometimes gets confused with other fungal or yeast skin problems that need a different approach. If your dog’s skin looks more greasy and inflamed than scaly and bald, it may be worth reading about yeast dermatitis in dogs instead, since the two conditions are treated quite differently.

How do you decontaminate your home?

Treating your dog is only half the job. Ringworm spores are tough: PDSA says they can survive on bedding, towels and grooming equipment for up to two years, and VCA’s vets put the figure at up to eighteen months. Either way, if you cure your dog but leave spores in the house, reinfection is a real risk.

Blue Cross recommends restricting your infected dog to one easy to clean room while they’re being treated, so spores don’t spread through the whole house. Vacuum soft furnishings and carpets thoroughly and often, or steam clean them, then empty the vacuum bag or canister straight into an outside bin rather than leaving it in the house. Wipe down hard surfaces with a disinfectant your vet recommends, and wash anything machine washable on a hot cycle. Bedding or toys that can’t be properly cleaned are often best replaced entirely.

For the bigger picture on how common skin problems are across UK dogs generally, see our UK dog skin statistics, and our skin, paw and nose care hub for related conditions worth knowing about.

Because several dog skin problems look alike from the outside, it is worth knowing how this compares to mange and a yeast infection, which can cause similar signs. When in doubt, a vet check settles it.