At the heart of ringworm are dermatophytes, which are fungi that cause skin infections (in this case, ringworm). Dermatophytes are keratinophilic, meaning they use the keratin in your skin as a fuel source.1,2 They can grow on humans, animals or in soil, and are highly contagious once they start spreading.
Since keratin is a protein specific to your skin only, ringworm won't infect your other body parts. The role of keratin is to hold skin cells together, forming the outermost layer that protects our internal organs from the outside world.3
Three types of dermatophytes cause ringworm, and they are classified by their asexual spores. In addition, the three types are broken down into different species. According to DermNet NZ, there are around 40 species of dermatophytes that can cause ringworm, but only 18 commonly appear among patients.4
The three dermatophytes responsible are Trichophyton (T.), Microsporum (M.), and Epidermophyton (E.). The table below shows the commonly recurring species of fungi that cause ringworm and how they are transmitted:5
Antrophilic (Humans to Humans)
Zoophilic (Animals to Humans)
Geophilic (Soil to Humans)
||M. canis (cats and dogs)
||T. equinum (horses)
||T. erinacei (hedgehogs)
||T. verrucosum (cattle)
||M. nanum (pigs)
||M. distortum (a variant of M. canis)
Circumstances That Cause Ringworm
Aside from anthrophilic, zoophilic and geophilic contact, other factors influence your chances of getting ringworm, such as your environment. Fungi thrive on heat and moisture, which are normally found in public locker rooms and showers, hence the sports-related nicknames of ringworm such as "athlete's foot" and "jock itch."
Another factor that can raise your chances of getting ringworm is a weakened immune system due to a current health condition. To prevent this, keep your health in optimal condition through proper diet and exercise, so your body can ward off fungi.
It also helps to be aware of the causes of ringworm so you can avoid them. One example: tinea pedis (aka athlete's foot)6 is usually caused by wearing occlusive footwear for extended periods of time. Occlusive footwear prevents air from circulating inside your shoes, and if coupled with excessive sweating, will produce an environment where ringworm-causing fungi can thrive.
Other times, carelessness is a cause for the spread of ringworm. For example, you may have fingernail ringworm, and it may spread to your scalp if you scratch your head. Your dog (or cat) may also infect you with ringworm if he recently came into contact with fungi-infected soil or animals. If your pet has ringworm, take him to the vet immediately to receive antifungal treatment.
How Long Does Ringworm Last?
Ringworm has an incubation period of four to 14 days before symptoms appear, so you might not know you have it already until the rashes appear. Fortunately, ringworm is curable, and the spreading and contagiousness stop within 24 to 48 hours once you start treatment.
Before going through any sort of treatment, though, it's important to have a doctor look into your rashes, because ringworm can be confused with other skin diseases. If you're given the wrong treatment, your ringworm may get even worse.