Ringworm: the fungal infection of skin, hair, and nails
Ringworm is a fungal infection caused by organisms called dermatophytes. The name refers to the circular appearance of some skin lesions, not to a worm living beneath the skin. Several fungal groups can cause it, including Trichophyton, Microsporum, and Epidermophyton. Dermatophytes can infect the skin, hair, and nails. The same broad group of organisms therefore produces conditions with different everyday names and appearances, depending on the part of the body involved. Athlete's foot is one familiar example of a dermatophyte infection, and scalp ringworm is another.
Medical names often combine tinea with a Latin term for the affected area. Tinea pedis involves the feet, tinea cruris the groin, and tinea capitis the scalp. Tinea corporis refers to body skin outside several separately named sites, including the hands, feet, face, and scalp. The location name does not identify the fungal species. A species can be associated with more than one site, and related species can produce similar appearances. A fungal infection of the nails is called onychomycosis; yeasts and other fungi can cause it as well as dermatophytes.
The CDC's Ringworm Basics page, reviewed in January 2026, describes an itchy, scaly, often ring-shaped rash that typically looks red on light skin and gray or brown on darker skin. On body skin, a lesion often begins as a circular patch with a scaly edge that expands outward. The center can become less inflamed while the advancing rim remains prominent, creating the ring-like outline. Several patches can eventually meet. Scalp and nail infections do not necessarily form an obvious ring. Nail involvement can instead produce discoloration, thickening, and increased brittleness.
The same CDC page lists skin-to-skin contact with people or animals, shared objects such as towels and bedsheets, and shared surfaces such as locker room or public bathroom floors among the ways ringworm spreads. Warm, damp conditions facilitate spread. Infection can also move from one part of a person's body to another. DermNet's tinea corporis page, updated in November 2020, gives an incubation period for this fungal infection of 1 to 3 weeks, while the appearance varies with the organism and site involved. People with weakened immune defenses can have more difficulty limiting infection.
Dermatophytes are grouped partly by their usual hosts. Anthropophilic species are associated with humans, zoophilic species with animals, and geophilic species with soil. Those categories describe ecological preferences, not barriers that prevent movement between hosts. Microsporum canis, for example, is associated with cats and dogs and can infect people. Some species linked with cattle, horses, or hedgehogs can also cause body ringworm. The distribution of particular organisms varies geographically, so the fungi commonly identified in one region may differ from those found most often elsewhere.
In ordinary body ringworm, the fungal infection spreads through the stratum corneum, the outermost skin layer. On healthy skin it generally remains superficial rather than entering deeper layers. Trichophyton rubrum is a common cause of tinea corporis worldwide. Close-contact sports provide a distinctive setting for transmission; tinea gladiatorum is the name used for infections associated with activities such as wrestling. That pattern is often linked with Trichophyton tonsurans. Other forms have different shapes, including the concentric rings of tinea imbricata associated with Trichophyton concentricum in tropical regions.
Scalp ringworm especially affects children before adolescence, though adults can develop it too. The fungi can invade a hair follicle and then the hair shaft. In an ectothrix infection, fungal spores occur outside the shaft; in an endothrix infection, they remain within it. These different growth patterns can affect how the hair looks and breaks. Fine scale and patchy hair loss are common features. Broken shafts can leave small dark points on the scalp, a pattern known as black-dot tinea. The organisms responsible differ between countries and populations.
DermNet's pages on tinea corporis and tinea capitis describe how laboratory examination can distinguish fungal structures from conditions that merely resemble ringworm. A skin scraping viewed under a microscope can reveal branching filaments called hyphae and fungal spores. Culture allows the organism to grow so its identity can be investigated. In scalp infection, clinicians can examine affected hairs as well as scale. DermNet notes that few fungi cause infected hairs to fluoresce under a Wood lamp. The absence of fluorescence consequently does not exclude all scalp dermatophytes. It describes culture as slow, taking up to 4 weeks.
The CDC's clinical overview for health care providers, reviewed in July 2024, says ringworm may be difficult to distinguish from other skin conditions, like psoriasis and eczema. The same overview calls emerging strains of dermatophytes causing severe ringworm a growing public health concern, and describes antimicrobial-resistant ringworm as emerging.
- CDC, Ringworm Basics — www.cdc.gov
- CDC, Clinical Overview of Ringworm — www.cdc.gov
- DermNet, Tinea corporis — dermnetnz.org
- DermNet, Tinea capitis — dermnetnz.org