You get ringworm from a dog through direct skin contact with an infected animal or by touching objects contaminated with fungal spores. Despite its name, ringworm isn’t caused by a worm. It’s a fungal infection that lives on the outer layer of skin and hair, and dogs are one of the most common sources of human cases. Symptoms typically appear 4 to 14 days after your skin comes in contact with the fungus.
How the Fungus Spreads to You
The fungus responsible for most dog-to-human ringworm cases is a species that naturally lives on dogs and cats. It colonizes the outer surface of an animal’s body, including skin, hair, and nails, and spreads to humans as a secondary infection. There are two main ways this happens.
The most common route is direct contact. Petting, grooming, bathing, or cuddling a dog that carries the fungus gives the spores an opportunity to transfer to your skin. Any area of exposed skin that touches the dog is vulnerable, which is why ringworm from pets often shows up on the arms, hands, face, and neck. The fungus doesn’t need broken skin to take hold. It feeds on keratin, the protein in your outer skin layer and hair, and can establish an infection on intact skin if conditions are right.
The second route is indirect contact through contaminated objects. Fungal spores shed from an infected dog’s coat onto bedding, furniture, carpets, brushes, collars, and clothing. These spores are remarkably hardy. Research on dermatophyte survival has shown that spores can remain viable for months on household surfaces at room temperature, and freeze-dried fungal cultures have been revived after 12 years with no loss of viability. That means a couch your dog slept on weeks ago can still be a source of infection.
Dogs That Look Healthy Can Still Spread It
One of the trickiest aspects of ringworm is that not every infected dog looks sick. Dogs can be asymptomatic carriers, meaning they harbor the fungus on their coat without developing visible skin problems. This is especially common toward the end of treatment, when a dog appears healed but still carries spores. Some dogs aren’t technically infected at all but simply have spores sitting on their fur, picked up from the environment, much like a couch might collect spores from a shedding animal.
When dogs do show symptoms, the signs include patches of hair loss, scaly or crusty skin, redness, small raised bumps, and darkened skin. Some dogs develop a swollen, nodular reaction called a kerion, often on the face or muzzle. Itching varies from mild to intense. Puppies and dogs with weakened immune systems tend to show more obvious signs, while healthy adult dogs may carry the infection with minimal or no visible clues.
What Ringworm Looks Like on You
After the 4-to-14-day incubation period, you’ll typically notice an itchy, ring-shaped rash. The hallmark is a raised, expanding circular border with a clearer or scaly center. On lighter skin, the ring appears red. On darker skin tones, it can look reddish, purplish, brown, or gray. The rash most often appears on the face, arms, and legs, but it can develop anywhere on the body.
As the infection progresses, you may see overlapping rings, cracked or scaly patches, or areas that become crusted or filled with pus. If the rash develops near your scalp or in a hairy area, you may notice hair falling out around the patch. The infection stays in the outer skin layers, so it doesn’t cause deep pain, but the itching can be persistent and uncomfortable.
Who Is More Likely to Get It
Anyone can catch ringworm from a dog, but some people are more susceptible. Children are at higher risk because they tend to have more close, physical contact with pets and their immune defenses are still maturing. People with weakened immune systems, whether from illness, medication, or chronic conditions, are also more vulnerable. Even minor skin damage like a scratch or dry, cracked skin can make it easier for spores to establish an infection.
Dog owners who groom or bathe their own pets have more frequent exposure to contaminated fur and skin flakes. Households with multiple pets face higher risk as well, since the fungus can circulate between animals before anyone shows symptoms.
Cleaning Your Home After Exposure
Because spores survive so long on surfaces, decontaminating your home is just as important as treating the infection itself. Effective cleaning requires two steps: first removing all organic matter (hair, skin flakes, dirt), then applying a disinfectant. Disinfectants won’t penetrate through a layer of grime, so vacuuming and wiping down surfaces first is essential.
Several common household products are effective against ringworm spores on pre-cleaned surfaces. These include accelerated hydrogen peroxide cleaners, potassium peroxymonosulfate products, and sodium hypochlorite-based sprays like Clorox Clean-Up. Quaternary ammonium disinfectants found in products like Formula 409, Fantastik, and Simple Green also work. The key is thorough, repeated cleaning of everything your dog contacts regularly: bedding, crates, floors, furniture, grooming tools, and soft furnishings.
Wash all pet bedding and any fabric your dog has touched in hot water. Vacuum carpets and upholstered furniture frequently, and dispose of the vacuum bag or empty the canister outside. Hard surfaces like tile and countertops are easier to decontaminate than porous materials like carpet or fabric, so focus extra attention on soft surfaces where spores can embed in fibers.
Reducing Your Risk
Wash your hands with soap and water after petting, grooming, or handling any dog, especially one you don’t know well. If your dog develops patches of hair loss, scaly skin, or crusty lesions, limit close contact until a veterinarian can evaluate them. Keep in mind that a negative visual check doesn’t guarantee a dog is spore-free, since carriers can look completely normal.
If someone in your household develops ringworm and you have a dog, get the dog examined even if it appears healthy. A veterinarian can comb the dog’s entire coat and culture the collected fur and skin to check for spores. Treating the animal and the environment simultaneously is the only reliable way to break the cycle of reinfection.