Ringworm (Tinea Corporis): What It Is and How to Treat It

What Is Ringworm?

Despite the name, ringworm has nothing to do with worms. It is a superficial (surface-level) fungal infection of the skin caused by a group of fungi called dermatophytes. These fungi feed on keratin—the protein that makes up the outer layer of your skin, hair, and nails.

The medical name, tinea corporis, means “fungal infection of the body” in Latin. “Tinea” refers to a fungal infection, and “corporis” refers to the body—as opposed to other forms of tinea that affect the feet (tinea pedis/athlete’s foot), the scalp (tinea capitis), or the groin (tinea cruris/jock itch).

The most common fungi responsible for ringworm are Trichophyton rubrum (60–70% of cases) and T. mentagrophytes (20–25%). In children, Microsporum canis—often caught from cats or dogs—is a frequent cause.

Signs and Symptoms

Ringworm is named for its characteristic appearance. Typical signs include:

• Round or oval patches of skin that are red and scaly at the outer edge, with central clearing—creating a ring-like appearance.
• Patches range from 1–5 cm in size (roughly half an inch to 2 inches).
• Well-defined, slightly raised borders.
• Mild to moderate itching in about 70% of cases.
• Most common on the arms, legs, and trunk; less common on the face.

Variations to be aware of:

• Tinea incognito: An atypical form that occurs when steroid cream has been mistakenly applied to ringworm. The ring shape disappears, leaving a poorly defined red patch that is harder to diagnose. Meanwhile, the fungus continues to grow beneath the surface.
• Kerion: A severe inflammatory reaction, most often seen in children infected with Microsporum species. Instead of a typical ring, the skin becomes swollen, pustular (full of pus), and may look like a bacterial abscess.
• Secondary bacterial infection: Scratching can introduce bacteria, occurring in about 5–10% of cases.

Causes and Risk Factors

Ringworm spreads through:

• Direct skin-to-skin contact with an infected person.
• Contact with infected animals—particularly cats and dogs. Zoonotic (animal-to-human) transmission accounts for about 15% of cases.
• Fomites—shared objects like towels, clothing, sports equipment, and locker room floors.
• Soil: Some dermatophytes live in soil and can infect people through prolonged ground contact.

Risk factors that make you more likely to develop ringworm or have a more severe infection:

• Diabetes: Elevated blood sugar creates a favorable environment for fungal growth in the skin.
• Obesity: Skin folds trap moisture and warmth, helping fungi thrive.
• Weakened immune system: HIV (especially with CD4 counts below 50), organ transplant recipients, and people on long-term steroid medications are at significantly higher risk.
• Warm, humid climates or environments: Tropical regions and sweaty locker rooms favor fungal growth.
• Age: Incidence peaks in children aged 2–8 years and again in teenagers and young adults aged 15–25 years.
• Shared athletic facilities: Gyms, locker rooms, and wrestling mats are common transmission sites.

How It’s Diagnosed

In most cases, a dermatologist can diagnose ringworm by examining the rash. Confirmation tests include:

• KOH (potassium hydroxide) preparation: Skin scrapings from the edge of the patch are treated with a chemical that dissolves skin cells but leaves fungal threads (hyphae) visible under a microscope. Sensitivity is 60–80% depending on technique.
• Fungal culture: The skin scraping is grown on a special medium in the laboratory to identify the exact fungal species. Results take 2–4 weeks but are highly accurate.
• Wood’s lamp (UV light) examination: Some fungi glow blue-green under UV light. However, 80% of ringworm-causing fungi do not fluoresce, limiting this test’s usefulness.
• Dermoscopy: A handheld magnifying tool used to examine the skin surface for spores and other clues.
• Skin biopsy with PAS stain: A special stain (periodic acid-Schiff) highlights fungal elements if the diagnosis is still uncertain after other tests.

Treatment Options

Treatment depends on how widespread the infection is.

For limited ringworm (fewer than 2 patches, less than 100 cm² total):

• Topical antifungal creams are the first-line treatment and work 80–90% of the time with consistent use.
• Clotrimazole 1% cream or miconazole 2% cream: Apply twice daily to the affected area and a 2 cm border around it for 4 weeks.
• Terbinafine 1% cream: Apply twice daily for 2–4 weeks; often effective in shorter courses.
• Continue applying cream for at least 1 week after the rash appears to have cleared to prevent recurrence.

For extensive ringworm (more than 2 patches, more than 100 cm², or facial involvement):

• Oral antifungal pills are needed when ringworm is too widespread for creams to cover.
• Terbinafine 250 mg daily for 2–4 weeks: The preferred agent in most guidelines, with about 90% efficacy and lower relapse rates than older options.
• Itraconazole 200 mg daily for 2–4 weeks: About 85% effective; a good alternative if terbinafine is not suitable.
• Fluconazole 150 mg once weekly for 2–4 weeks: An off-label option with around 80% efficacy and good tolerability.
• Griseofulvin 500–1000 mg daily for 4–6 weeks: An older medication that is largely replaced by newer options due to its longer treatment course and more side effects.

For severe inflammatory ringworm (kerion): A combination of oral antifungals and a short course of oral steroids (prednisolone) is often used to reduce severe swelling and prevent scarring.

What to Expect / Recovery

• With topical treatment, most limited infections clear within 2–4 weeks. Itching usually improves within the first few days of treatment.
• Oral antifungal therapy for extensive cases typically shows results within 1–2 weeks, with full clearance by the end of the treatment course.
• Some redness or skin darkening may persist for weeks after the fungus is gone—this is a normal part of healing.
• Do not stop treatment early, even if the rash looks better. Incomplete treatment is the most common cause of recurrence.
• Avoid sharing towels, clothing, or sports equipment during treatment.
• If a pet is the suspected source, have the animal evaluated by a veterinarian.

When to See a Dermatologist

See a dermatologist if:

• The rash has not improved after 2 weeks of using an over-the-counter antifungal cream correctly.
• The patches are large, numerous, or covering the face.
• The skin is becoming very swollen, painful, or discharging pus (possible kerion or bacterial infection).
• You are unsure whether the rash is ringworm, eczema, or another condition.
• You are immunocompromised—early and accurate treatment is especially important.
• You have used steroid cream on the area (which can mask the diagnosis and worsen the infection).

Frequently Asked Questions

Q: How long is ringworm contagious?
A: Ringworm is contagious as long as fungal spores are present on the skin—usually until 24–48 hours after starting effective antifungal treatment. To be safe, keep the area covered and avoid close skin-to-skin contact until the rash is clearly improving.

Q: Can I get ringworm from my cat or dog?
A: Yes. Animal-to-human transmission accounts for about 15% of ringworm cases. Kittens and puppies are the most common sources. If your pet has scaly patches on its skin or areas of hair loss, take it to a veterinarian for evaluation. Treatment of the animal helps prevent re-infection.

Q: Why did my ringworm get worse after I used hydrocortisone cream?
A: Steroid creams (like hydrocortisone) suppress the skin’s immune response, which can make the fungal infection spread more rapidly while making the rash look less like typical ringworm. This is called tinea incognito. If you applied a steroid cream to what turned out to be ringworm, it is important to see a dermatologist for proper diagnosis and antifungal treatment.

Q: Is ringworm dangerous?
A: In otherwise healthy people, ringworm is a surface skin infection that is treatable and not dangerous. In people with severely weakened immune systems, the infection can be more extensive and harder to treat, but it still responds to antifungal medications. Untreated or mismanaged ringworm can occasionally develop secondary bacterial infection, which would require antibiotic treatment.