Definition and epidemiology
Tinea cruris is a dermatophytosis (superficial fungal infection of keratinized tissue) involving the groin, perineum, perianal skin, and proximal medial thighs. It is one of the most common forms of dermatophyte infection worldwide.
- Peak incidence in adolescent and adult males; much less common in women and prepubertal children.
- Strongly associated with tinea pedis ("two feet, one hand" type spread via fomites, towels, or autoinoculation from feet to groin).
- More frequent in hot, humid climates and summer months.
- Occlusive clothing, obesity, and participation in contact sports or communal athletic facilities increase risk.
- Immunosuppression (diabetes mellitus, HIV, corticosteroid use) increases incidence and severity.
- Scrotum is classically spared in tinea cruris — key distinguishing feature from candidal intertrigo.
- Most common causative organism: Trichophyton rubrum.
- KOH prep shows septate branching hyphae at the active, scaly, advancing border.
- Wood's lamp is NOT useful here (unlike erythrasma, which fluoresces coral-red).
- Always check feet for tinea pedis — common reservoir and source of autoinoculation.
- Avoid prolonged combination steroid-antifungal creams — risk of tinea incognito.
- First-line treatment is topical azole or allylamine antifungal, not oral therapy, for localized disease.
- Candida intertrigo shows satellite pustules and scrotal involvement; tinea cruris does not.
Etiology and risk factors
Causative organisms
- Trichophyton rubrum — most common cause.
- Trichophyton mentagrophytes and Epidermophyton floccosum — also frequent causes.
- Zoophilic species (e.g., Microsporum canis) are rare causes and tend to produce a more inflammatory reaction.
Risk factors
- Excessive sweating (hyperhidrosis) and warm, humid environment.
- Tight or occlusive clothing, synthetic underwear.
- Shared locker rooms, gyms, communal showers.
- Concurrent tinea pedis or onychomycosis (reservoir for autoinoculation).
- Obesity (increased skin-fold occlusion and friction).
- Diabetes mellitus and other immunocompromised states.
- Male sex (scrotal skin is more resistant to invasion than inguinal skin, but the warm moist environment of the groin favors infection of surrounding skin).
Pathophysiology
Dermatophytes are keratinophilic fungi that secrete keratinases, allowing them to digest and colonize the stratum corneum, hair, and nails without invading living tissue. Infection is typically acquired by direct contact with infected skin, fomites (towels, clothing), or autoinoculation from a pre-existing tinea pedis or onychomycosis.
The fungus proliferates centrifugally within the stratum corneum. The advancing edge represents the area of active fungal growth and maximal host inflammatory response (erythema, scale, vesiculation), while the central area clears as the organism exhausts local keratin and the immune response subsides, producing the classic annular "ring" appearance. Heat, moisture, and occlusion in the groin create an ideal environment for fungal growth and friction worsens barrier disruption. The scrotum is usually spared because of its unique anatomy and ability to disperse heat and moisture, which is a key clinical distinguishing feature from candidal intertrigo.
Clinical features
- Pruritic, erythematous to red-brown patch or plaque in the groin, extending to the inner thigh and sometimes the gluteal cleft or lower abdomen.
- Well-demarcated, raised, scaly, advancing border with central clearing (annular configuration).
- Bilateral but often asymmetric involvement.
- Scrotum and penis are classically spared — an important distinguishing feature from candidiasis.
- Chronic lesions may show lichenification from scratching.
- Look for concomitant tinea pedis or onychomycosis (common source of infection).
- Maceration, secondary bacterial infection, or id reaction (autoeczematization) can occur in longstanding or irritated cases.
Diagnosis
Diagnosis is primarily clinical, confirmed by microscopy when needed.
Potassium hydroxide (KOH) preparation
- Scrape scale from the active advancing border.
- KOH mount shows septate, branching hyphae crossing skin cell borders — diagnostic of dermatophyte infection.
Fungal culture
- Not routinely required but useful if diagnosis is uncertain or treatment fails; identifies the specific dermatophyte species.
Wood's lamp examination
- Generally not useful for tinea cruris (dermatophytes causing tinea cruris do not fluoresce), unlike some cases of tinea capitis.
Additional tips
- Always examine the feet and nails for a source infection.
- Biopsy with PAS stain is reserved for atypical or refractory presentations.
Differential diagnosis
| Condition | Distinguishing feature |
|---|---|
| Candidal intertrigo | Scrotum/penis involved, satellite pustules, no central clearing, beefy-red |
| Erythrasma | Coral-red fluorescence under Wood's lamp (Corynebacterium minutissimum), fine scale, no central clearing |
| Inverse psoriasis | Well-demarcated, glazed/shiny erythema, often symmetric, nail pitting or psoriasis elsewhere |
| Contact/irritant dermatitis | Lacks advancing scaly border, history of new soap/detergent exposure |
| Seborrheic dermatitis | Greasy yellow scale, also affects scalp, nasolabial folds |
| Lichen simplex chronicus | Lichenified plaque from chronic scratching, no central clearing or active border |
Management
General measures
- Keep the area clean and dry; loose, breathable (cotton) underwear.
- Dry groin thoroughly after bathing/exercise; dry feet before groin to avoid cross-contamination.
- Treat any concurrent tinea pedis or onychomycosis simultaneously to prevent reinfection.
- Avoid sharing towels or clothing.
Pharmacologic treatment
First-line — topical antifungals (limited disease), applied once to twice daily for 2-4 weeks, continued at least 1 week after visible clearing:
- Allylamines: terbinafine cream (shorter courses, fungicidal).
- Azoles: clotrimazole, miconazole, ketoconazole, econazole.
- Avoid combination topical steroid-antifungal creams for prolonged use — steroids can mask inflammation, promote fungal proliferation, and cause tinea incognito.
Oral antifungals — reserved for extensive disease, treatment failure, recurrent infection, or immunocompromised patients:
- Terbinafine (oral) or itraconazole; fluconazole is an alternative.
- Griseofulvin is less preferred due to longer treatment courses and lower efficacy against T. rubrum compared to newer agents.
Guideline notes
Most US and European dermatology guidelines agree topical therapy is sufficient for localized tinea cruris, reserving systemic antifungals for widespread, recalcitrant, or immunosuppressed cases. There is no universally mandated specific agent; selection is based on availability, cost, and patient adherence.
Complications and prognosis
- Generally an excellent prognosis with appropriate antifungal therapy; most cases resolve within 2-4 weeks.
- Recurrence is common, especially without addressing predisposing factors (moisture, occlusive clothing, untreated tinea pedis).
- Tinea incognito: altered, less distinct presentation due to inappropriate topical corticosteroid use, which can delay diagnosis and worsen infection.
- Secondary bacterial superinfection from scratching.
- Post-inflammatory hyperpigmentation, particularly in darker skin types.
- Chronic or treatment-resistant infection should prompt evaluation for an underlying immunocompromised state (e.g., diabetes, HIV) or confirmation of diagnosis via culture.
"Groin ring, scrotum spared, feet to blame" — remember the annular ring-shaped border, scrotal sparing distinguishing it from Candida, and the foot as the usual source of infection.
Practice questions
1. A 24-year-old male soccer player presents with a two-week history of an itchy rash in both groin creases extending to the inner thighs. Examination reveals a well-demarcated, scaly, erythematous plaque with a raised border and central clearing. The scrotum appears normal. Which of the following is the most likely causative organism?
2. A 35-year-old man with tinea cruris was treated for three weeks with a combination clotrimazole-betamethasone cream purchased over the counter. His rash initially improved but has now become more widespread with less distinct borders and persistent redness. KOH examination still shows hyphae. What is the most likely explanation for this presentation?
3. A 45-year-old man with poorly controlled type 2 diabetes presents with a widespread, treatment-resistant groin rash that has not responded to six weeks of topical terbinafine. KOH prep confirms dermatophyte infection. Which of the following is the most appropriate next step in management?
Frequently asked questions
What causes tinea cruris?
Tinea cruris is caused by dermatophyte fungi, most commonly Trichophyton rubrum, which infect the keratin layer of groin skin. Infection usually spreads from the feet (tinea pedis) via autoinoculation, fomites like towels and shared clothing, or direct skin contact. Risk is increased by heat, sweating, occlusive clothing, obesity, and immunosuppression such as diabetes.
What are the first symptoms of tinea cruris?
The first symptoms are itching and mild redness in the groin crease, which progresses to a well-defined, scaly, red-brown patch with a raised, advancing border and central clearing. The rash typically extends onto the inner thigh and spares the scrotum and penis. Discomfort worsens with sweating, heat, and friction from clothing.
How is tinea cruris diagnosed?
Diagnosis is usually clinical, based on the characteristic annular, scaly plaque with scrotal sparing. When confirmation is needed, a KOH preparation of skin scraping from the active border shows septate branching hyphae. Fungal culture is reserved for uncertain or treatment-resistant cases, and Wood's lamp examination is not useful for this condition.
Is tinea cruris curable?
Yes, tinea cruris is fully curable with appropriate topical or, in extensive cases, oral antifungal therapy, usually within 2 to 4 weeks. However, recurrence is common if predisposing factors such as moisture, tight clothing, or untreated tinea pedis are not addressed. Completing the full treatment course even after symptoms resolve reduces relapse.
Tinea cruris vs candidal intertrigo — what is the difference?
Tinea cruris spares the scrotum and shows a well-demarcated, scaly, advancing border with central clearing, while candidal intertrigo typically involves the scrotum, lacks central clearing, and features beefy-red erythema with satellite pustules at the edges. KOH prep differentiates them: septate hyphae in tinea cruris versus budding yeast with pseudohyphae in candidiasis.
Key drugs
Related conditions and differentials
Sources and further reading
StatPearls (NCBI Bookshelf)MedlinePlusWHO ICD-10: B35.6
Educational content for medical students, prepared by the WhiteCoat Pro editorial team with AI assistance; every page is reviewed by a second AI model for factual errors. It is not medical advice and does not replace the product label, local guidelines or a clinician.