Tinea and Candida are both fungal but behave differently. Distribution and morphology distinguish them — and treatment differs. KOH preparation is the diagnostic test. Never apply topical steroids to an undiagnosed rash — tinea incognito is the result.
CLINICAL PRINTABLE
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1 · Interpretation Framework
- Tinea (dermatophytosis): fungal infection of keratinized structures (skin, hair, nails) by dermatophytes (Trichophyton, Microsporum, Epidermophyton). Named by body site: tinea pedis (feet), tinea cruris (groin), tinea corporis (body), tinea capitis (scalp), tinea unguium/onychomycosis (nails), tinea versicolor (Malassezia — technically not a dermatophyte).
- Tinea morphology: annular (ring-shaped) plaque with central clearing and an active, scaly, advancing border. Pruritic. Tinea pedis (athlete's foot) presents with maceration, scaling, and fissuring of the toe web spaces — the most common portal of entry for lower extremity cellulitis.
- Candida (cutaneous candidiasis): caused by Candida albicans and other Candida species. Prefers warm, moist, occluded skin folds (intertriginous areas): groin, axillae, inframammary folds, abdominal pannus, perianal area, diaper area. Presents with erythematous plaques with satellite papules and pustules — the satellite lesions are characteristic.
- Tinea versicolor (pityriasis versicolor): caused by Malassezia furfur. Presents with hypo- or hyperpigmented macules and patches on the trunk and upper arms. Scaling is fine. Common in warm, humid climates and in young adults. Recurrence is common.
- KOH preparation: the diagnostic test for fungal skin infections. Scrape the active border of the lesion, apply KOH, and examine under microscopy. Hyphae (tinea) or pseudohyphae/budding yeast (Candida) confirm the diagnosis. Tinea versicolor shows the classic 'spaghetti and meatballs' pattern.
- Risk factors for Candida: diabetes mellitus, obesity, immunosuppression, antibiotic use (disrupts normal flora), incontinence, occlusive dressings, and prolonged moisture exposure.
2 · Nuance That Changes Interpretation
Tinea incognito
Tinea treated with topical corticosteroids loses its classic annular appearance — the border becomes less distinct, the scale disappears, and the rash spreads. This is tinea incognito. Always consider fungal infection before prescribing topical steroids for an undiagnosed rash. KOH preparation is essential.
Onychomycosis treatment duration
Nail fungal infections require prolonged systemic antifungal therapy: terbinafine 250 mg daily for 6 weeks (fingernails) or 12 weeks (toenails). Topical antifungals have poor nail penetration and limited efficacy for onychomycosis. Liver function monitoring is recommended for systemic terbinafine.
Candida vs tinea in the groin
Both tinea cruris and cutaneous candidiasis affect the groin. Tinea cruris has a well-defined, scaly, advancing border and typically spares the scrotum. Candida has satellite lesions and often involves the scrotum and perianal area. KOH distinguishes them — treatment differs (azole vs. terbinafine).
Recurrence prevention
Tinea pedis recurs without addressing the reservoir: treat shoes (antifungal powder), use moisture-wicking socks, dry between toes after bathing. Tinea versicolor recurs in warm weather — maintenance therapy (monthly ketoconazole shampoo or selenium sulfide) reduces recurrence.
Systemic antifungals and drug interactions
Azole antifungals (fluconazole, itraconazole, ketoconazole) are CYP3A4 inhibitors with significant drug interactions: warfarin (increased INR), statins (myopathy risk), calcineurin inhibitors (tacrolimus, cyclosporine toxicity). Review the medication list before prescribing systemic azoles.
3 · What Should Raise Concern
- Tinea capitis in adults — uncommon and should prompt consideration of immunocompromise. Requires systemic antifungal therapy (topical agents do not penetrate the hair follicle).
- Widespread or rapidly spreading cutaneous candidiasis — consider systemic candidiasis, especially in immunocompromised patients. Blood cultures and systemic antifungal therapy may be required.
- Kerion (inflammatory tinea capitis) — boggy, tender scalp mass with pustules and hair loss. Requires systemic antifungal therapy and may require systemic corticosteroids to reduce scarring alopecia.
- Tinea treated with topical steroids (tinea incognito) — the rash spreads and loses its classic appearance. Discontinue steroids, confirm with KOH, and treat with appropriate antifungal.
4 · What Do I Do Next?
- Confirm the diagnosis with KOH preparation before starting antifungal therapy — especially when the presentation is atypical or the rash has been treated with topical steroids.
- Choose the correct antifungal: terbinafine (allylamine) is fungicidal and preferred for tinea; azoles (clotrimazole, miconazole, fluconazole) are fungistatic and preferred for Candida.
- Treat the reservoir and risk factors: tinea pedis (shoes, socks, drying technique), Candida (moisture control, diabetes management, incontinence care).
- For onychomycosis: confirm with KOH or nail culture before starting systemic therapy. Check LFTs before and during systemic terbinafine.
- Review drug interactions before prescribing systemic azoles — warfarin, statins, and calcineurin inhibitors are common interactions.
Apply It · Patient Cases
CASE 1
A 32-year-old presents with a pruritic, annular, scaly rash on the inner thigh. The border is active and advancing; the center is clearing. KOH shows hyphae. Tinea cruris is diagnosed. Topical terbinafine cream twice daily for 2 weeks is prescribed. He is counseled to keep the area dry and to treat concurrent tinea pedis.
CASE 2
A 68-year-old with poorly controlled diabetes presents with erythematous plaques in the inguinal folds and perianal area with satellite papules and pustules. KOH shows pseudohyphae and budding yeast. Cutaneous candidiasis is diagnosed. Topical clotrimazole cream is prescribed, and diabetes management is optimized.
NOW CHANGE ONE DETAIL
Same patient as Case 1, but he was previously treated with triamcinolone cream for 3 weeks. The rash has spread beyond the thigh and lost its classic annular appearance. Tinea incognito is suspected. KOH confirms hyphae. The steroid is stopped and topical terbinafine is started — the rash resolves over 4 weeks.
Bottom Line
Tinea prefers dry keratinized surfaces and has an active scaly border. Candida prefers moist skin folds and has satellite lesions. KOH confirms both. Never apply topical steroids to an undiagnosed rash — tinea incognito is the result.
EVIDENCE & REFERENCES
- Ely JW, et al. Diagnosis of Tinea. Am Fam Physician. 2014;90(10):702–710. https://www.aafp.org/pubs/afp/issues/2014/1115/p702.html
- Pappas PG, et al. Clinical Practice Guideline for the Management of Candidiasis: 2016 Update by IDSA. Clin Infect Dis. 2016;62(4):e1–50. doi:10.1093/cid/civ933
- Gupta AK, et al. Onychomycosis: a review. J Eur Acad Dermatol Venereol. 2020;34(9):1972–1990. doi:10.1111/jdv.16394