Ringworm spreads through direct contact with an infected person, animal, or contaminated surface. Despite the name, it’s not a worm at all. It’s a fungal infection caused by organisms called dermatophytes that feed on keratin, the tough protein in your skin, hair, and nails. You can pick it up from surprisingly common, everyday situations, and the fungal spores responsible can survive on surfaces for up to 20 months.
What the Fungus Actually Does
Dermatophytes are uniquely adapted to live on skin. They produce a chemical called sulfite that breaks apart the bonds holding keratin together, essentially dissolving the outermost layer of your skin to use as food. This is why the infection stays superficial: the fungus doesn’t invade deep tissue, but it thrives on the dead outer layer of skin, hair shafts, and nails. The characteristic ring-shaped rash forms as the fungus spreads outward from the initial point of contact while the center begins to heal.
Symptoms typically appear 4 to 14 days after your skin contacts the fungus. That delay matters because people and animals can spread it before anyone realizes an infection is present.
Person-to-Person Contact
Skin-to-skin contact with someone who has an active infection is the most straightforward way to catch ringworm. This is especially common in contact sports. Wrestlers deal with it so frequently that the condition has its own clinical name in that context: tinea corporis gladiatorum. Any sport involving grappling, close holds, or shared mats carries elevated risk.
Sexual contact can also transmit ringworm. A CDC case report documented a strain called Trichophyton indotineae spreading through sexual contact, causing lesions on the inner thigh, genitals, and buttocks. This particular strain, which has been spreading globally from southern Asia, is resistant to the most commonly used antifungal treatment (terbinafine) and spreads easily between people.
Animals Are a Major Source
Cats, dogs, cattle, and other animals carry dermatophyte fungi and can pass them to humans through petting, grooming, or handling. Cats are particularly common carriers and sometimes show no visible symptoms, making them silent sources of infection. Kittens and puppies are more likely to be infected than adult animals. If you adopt a new pet or spend time around livestock, any unexplained circular rash in the weeks afterward is worth investigating.
Contaminated Surfaces and Objects
Fungal spores shed from infected skin or hair land on surfaces and remain viable for 12 to 20 months. That’s an extraordinarily long survival time, and it means you can catch ringworm from objects and environments long after the infected person or animal has left.
Common culprits include:
- Shared personal items: towels, combs, brushes, hats, and clothing
- Gym and locker room surfaces: shower floors, benches, yoga mats, and shared sports equipment
- Household surfaces: bedding, couches, carpets, and floors where pets rest
Walking barefoot in locker rooms, public showers, and pool areas is a classic route for picking up foot ringworm (athlete’s foot), which can then spread to other parts of your body through touch.
Soil Contact
A small number of dermatophyte species live in soil, feeding on decomposing keratin from shed skin and hair. The most notable one, Microsporum gypseum, can infect humans through direct soil contact. This route is less common than catching it from people or animals, but gardeners and anyone working in dirt with bare hands or open skin abrasions should be aware of the possibility.
Conditions That Raise Your Risk
Not every exposure leads to infection. The fungus needs the right conditions to take hold. A humid environment, sweaty or macerated skin, and superficial scrapes or abrasions all increase the odds. Tight, occlusive clothing that traps moisture against the skin creates an ideal growth environment, which is why athletes in heavy gear are disproportionately affected.
Tropical and warm climates carry higher baseline risk simply because heat and humidity favor fungal growth. Living in close quarters, lacking air conditioning, and having known contact with infected individuals all compound the risk further. Children are more susceptible than adults, partly because of close contact in schools and daycare settings.
How to Reduce Transmission
Prevention comes down to limiting spore exposure and keeping your skin dry and intact. Wear sandals or shower shoes in locker rooms, public showers, and pool decks. Avoid sharing towels, combs, hats, or clothing. If someone in your household has ringworm, wash their laundry separately from everyone else’s. You don’t need bleach or scalding water for this. Regular detergent works, but don’t overfill the machine, because mechanical agitation is what physically removes the spores. Dry contaminated laundry on high heat and clean the lint filter after every load. Bedding or soft items that can’t be machine washed should be thrown away.
Frequently disinfect shared surfaces in your home during an active infection, especially floors and bathroom surfaces. If you have pets showing bald patches, scaly skin, or broken hair, get them evaluated and treated promptly, because they’ll continue shedding spores into your environment until the infection clears. Even asymptomatic cats can be carriers, so a vet check is worthwhile if household members keep getting reinfected with no obvious source.
The Resistant Strain Worth Knowing About
Trichophyton indotineae is a relatively new dermatophyte species that has been causing widespread, hard-to-treat outbreaks, primarily originating in southern Asia but now reported in multiple U.S. states and other countries worldwide. It spreads easily between people, tends to cause extensive rashes on the face, body, and groin, and is frequently resistant to terbinafine, the go-to oral antifungal for ringworm. Infections with this strain often require alternative medications and longer treatment courses. If you develop ringworm that doesn’t respond to standard treatment, or if you’ve recently traveled to South or Southeast Asia, that context is important information to share with your healthcare provider.