Fungal skin infections: athlete's foot, ringworm, yeast, and what's NOT fungus

Superficial fungal skin infections are among the most common conditions a person will manage without a clinic in prolonged austere scenarios — highly treatable with inexpensive topical medications, but genuinely disabling if ignored for weeks. Wet boots, sweat, shared bedding, and disrupted hygiene routines create exactly the conditions fungi need to spread. The harder problem is that fungal infections mimic several more dangerous conditions, and the reverse is equally true: bacterial cellulitis regularly gets mistaken for an "obvious" fungal rash, and that delay — antibiotics started days late — is how manageable wound infections become sepsis.

Educational use only

This page provides general educational information for emergency preparedness scenarios when professional medical care is unavailable. It is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of a qualified healthcare provider. Use this information at your own risk.

Before you start

Materials: Clotrimazole 1% cream OR terbinafine 1% cream (primary topical antifungal); antifungal powder (miconazole 2% or undecylenic acid) for footwear and prophylaxis; soap; at least two pairs of moisture-wicking socks in rotation; clean towels per person. See medical stockpiling for stocking guidance.

Know before you treat: Tinea capitis (scalp ringworm) in children requires an oral antifungal — topicals do not penetrate the hair shaft. FDA-approved terbinafine oral granules dosing (children ≥4 years) × 6 weeks: <25 kg: 125 mg daily; 25–35 kg: 187.5 mg daily; >35 kg: 250 mg daily (target ~5–8 mg/kg/day); children <4 years or <11 kg require pediatric specialist guidance. Griseofulvin 20–25 mg/kg/day micronized × 6–12 weeks remains the standard for Microsporum species per AAFP Common Tinea Infections guidelines.

Conditions: Apply to dry skin. Skin that is wet or damp at application time reduces drug absorption. Dry the area completely — including between the toes — before applying any topical antifungal.

Action block

Do this first: Apply clotrimazole 1% or terbinafine 1% cream to the affected area twice daily, covering the rash plus 1–2 cm (0.4–0.8 in) of surrounding skin. Time required: Active: 2–3 minutes twice daily; duration: 1–4 weeks depending on agent and syndrome. Cost range: Inexpensive — clotrimazole and miconazole are over-the-counter generics. Terbinafine OTC is similarly inexpensive. Skill level: Beginner — no clinical training required for diagnosis or topical treatment. Tools and supplies: Topical antifungal cream; clean towel; antifungal powder for footwear or skin folds (optional but useful in wet conditions). Safety warnings: See When "fungal-looking" is actually dangerous below — spreading, hot, painful redness with fever is bacterial cellulitis; topicals will not stop it.

The five fungal-skin syndromes you will actually encounter

Each syndrome below has a distinct anatomic location, characteristic appearance, and treatment course. Knowing the pattern prevents both missed fungal infections and misidentification of more serious conditions.

Tinea pedis (athlete's foot)

Where: Between the toes and on the soles and sides of the feet. The web space between the fourth and fifth toes is the earliest and most common site.

What it looks like: Itchy, scaly, sometimes peeling or blistered skin. Chronic cases produce a dry, diffuse scaling across the sole ("moccasin" pattern). Severely macerated interdigital spaces can turn white and soft with a distinct odor. Chronically wet boots are the single most reliable accelerant.

Treatment: Terbinafine 1% cream once daily × 1 week, or clotrimazole 1% cream twice daily × 2–4 weeks per CDC ringworm treatment guidance. Apply to the affected area and the surrounding 1–2 cm (0.4–0.8 in) of normal skin. Dry feet completely before applying.

Adjunct care: Rotate boot pairs (at least two) so the off-pair airs for 24 hours. Use antifungal powder in footwear and socks. Change socks daily minimum; more frequently in wet conditions.

Tinea corporis (ringworm)

Where: Trunk and limbs. Ringworm has nothing to do with worms — the name refers to the shape.

What it looks like: Ring-shaped patch with a scaly, slightly raised outer border and central clearing. The active border is where the fungus is expanding; the center clears as the immune response catches up. Multiple rings may overlap. Intensely itchy.

Transmission: Direct skin contact with an infected person, animal (cats and dogs are common reservoirs), or contaminated fomites (towels, helmets, bedding). In a shelter-in-place or group-living scenario, transmission is rapid if shared items are not controlled.

Treatment: Clotrimazole 1% cream or terbinafine 1% cream, twice daily × 2–4 weeks. Cover the lesion during the day to reduce fomite spread. Wash bedding and shared clothing at high heat — above 130°F (54°C) — to kill spores. Treat household contacts if exposure was shared.

Tinea cruris (jock itch)

Where: Groin folds, inner thighs, and the crease where the thigh meets the body. Characteristically spares the scrotum and penis — this anatomic boundary is a key differentiator from candidal intertrigo (see below, which does involve those structures).

What it looks like: Itchy, scaly, red patches with a sharply defined, raised border. Accelerated by sweat, heat, and tight clothing. Common in anyone spending long hours in wet gear.

Treatment: Topical antifungal cream (clotrimazole 1% or terbinafine 1%) twice daily × 2–4 weeks. Loose, breathable clothing. Dry the area thoroughly after bathing. Change underwear daily. Applying antifungal powder to the groin after drying is an inexpensive prophylactic measure in chronically sweaty conditions.

Candida intertrigo (yeast)

Where: Skin folds — groin, under breasts, abdominal fold in overweight individuals, sometimes between toes or fingers. Unlike tinea cruris, candidal infection actively involves the scrotum and penis (or labia in women). This location is the single most reliable field differentiator.

What it looks like: Bright red, moist, occasionally eroded skin at the fold. The classic finding is satellite pustules — small red pustules or papules dotting the skin just beyond the main rash edge. These satellites indicate Candida and rarely appear in tinea infections.

Risk factors: Diabetes significantly increases candidal skin infection risk. Obesity, antibiotic use disrupting normal flora, occlusive dressings, incontinence, and immunocompromised states all contribute. In a prolonged scenario, any diabetic with skin-fold redness should be treated as candidal until proven otherwise.

Treatment: Clotrimazole 1% cream or nystatin cream twice daily × 2–4 weeks. Note: nystatin works for Candida only and has no effect on tinea (dermatophyte) infections. Clotrimazole covers both. Keep the area dry — a thin layer of zinc oxide paste applied over the antifungal cream creates a moisture barrier in severe cases. For resistant cases in immunocompromised hosts, oral fluconazole 150 mg single dose or a weekly course may be necessary.

Tinea capitis (scalp ringworm)

Who gets it: Almost exclusively children. Adults rarely contract tinea capitis because post-pubertal sebum has antifungal properties.

What it looks like: Scaly patches on the scalp with patchy hair loss. May appear as "black dot" pattern (broken hairs at the follicle) or kerion (a painful, swollen, boggy mass with pus — a severe inflammatory response that can cause permanent scarring). Sometimes misidentified as severe dandruff.

Critical treatment distinction: Topical antifungals do not penetrate the hair shaft. Oral therapy is required.

  • Terbinafine (preferred for Trichophyton species, which cause most North American cases) × 6 weeks per FDA-approved Lamisil Oral Granules dosing for children ≥4 years: <25 kg: 125 mg daily; 25–35 kg: 187.5 mg daily; >35 kg: 250 mg daily (approximates ~5–8 mg/kg/day target). The middle 25–35 kg band is clinically important — using the adult 250 mg dose in a 28 kg child is a mild overdose; using 125 mg is an under-dose with higher relapse risk.
  • Griseofulvin (preferred for Microsporum species): 20–25 mg/kg/day micronized × 6–12 weeks

Selenium sulfide 2.5% or ketoconazole 2% shampoo used two to three times per week reduces spore shedding and limits household spread, but it does NOT replace oral therapy.

If oral antifungals are unavailable, prioritize evacuation to a clinician. Untreated kerion causes permanent hair follicle scarring. Any child with scalp scaling and hair loss should be presumed tinea capitis until proven otherwise.

Onychomycosis (nail fungus)

What it looks like: Thickened, yellow-brown or white, brittle, crumbling nail. Toenails are affected far more often than fingernails. The nail may separate from the nail bed (onycholysis). One nail is often the index case, spreading over months to adjacent nails.

Significance: Mostly cosmetic in healthy individuals. Elevated risk in diabetics — onychomycosis disrupts the nail's protective barrier, creating an entry point for bacterial superinfection and, in severe cases, contributing to the pathway toward foot ulcer and amputation. Painful nails are also a foot-mobility problem in an operational scenario.

Treatment:

  • Topical: Efinaconazole 10% solution once daily × 48 weeks (fingernails) / 52 weeks (toenails) is effective but requires a prescription and is expensive. OTC topical options have minimal penetration and low cure rates in established disease.
  • Oral (effective): Terbinafine 250 mg daily × 6 weeks (fingernails) / 12 weeks (toenails) — cure rates 70–80% for toenails with this regimen.
  • Oral pulse fluconazole: 150–300 mg once weekly × 3–6 months (fingernails) / 6–12 months (toenails). Fluconazole concentrates in nail keratin with a long half-life, making once-weekly dosing clinically effective per evidence-based reviews (Gupta 2012, J Dermatol Treat). This is the regimen corrected in the pathogen primer based on medical-sme review — not daily dosing.

Escalation priority for onychomycosis: diabetics or anyone with painful, functionally limiting nails. Healthy individuals can defer oral therapy until professional care is accessible.

When "fungal-looking" is actually dangerous

This is the inverse problem Codex flagged and the reason this page exists: multiple conditions look like fungal rashes and are not. Treating bacterial cellulitis as athlete's foot while the redness spreads toward a lymph node is a potentially lethal delay. Treating contact dermatitis with antifungal cream for two weeks misses the allergen and prolongs the rash needlessly.

Use the decision table below. The critical differentiators — fever, speed of spread, scaly border, satellite pustules, prior exposure, anatomic location — separate the categories.

Condition Key features What it's NOT Action
Cellulitis Red, spreading, hot, painful, often NO scaly border or central clearing; fever; follows wound or insect bite; usually one limb Not fungal Systemic antibiotics per wound infection STONES assessment — topicals are useless
Contact dermatitis Well-defined geometric border matching a contact area (watch strap, waistband, plant); intense itch; NOT scaly in the same pattern as ringworm; history of new product or plant exposure Not fungal Remove allergen; hydrocortisone 1% cream × 5–7 days for itch
Atopic eczema Chronic, recurrent, flexural surfaces in adults (inner elbow, behind knee); cheeks and extensors in young children; itch out of proportion to visible redness; positive personal or family allergy history Not fungal Emollients + low-potency topical steroid; eczema is a chronic barrier defect, not an infection
Psoriasis Silvery-white, well-demarcated plaques typically on elbows, knees, and scalp; may have nail pitting; present for months to years; positive family history common Not fungal Topical steroids, calcipotriene; chronic condition requiring ongoing management
Erythema migrans (Lyme) Expanding ring-shaped rash after tick exposure; usually warm but NOT scaly; centrally pale or clearing; grows to >2 inches (5 cm) and beyond; painless in most cases; single lesion typical May look like ringworm — it is NOT Prophylactic or therapeutic doxycycline — see tick bite management. No antifungal
Nummular eczema Coin-shaped, very itchy, scaly patches on limbs; may have subtle central clearing; no identified contact allergen May look like ringworm Trial 2-week topical antifungal if uncertain — improvement suggests tinea; no improvement suggests nummular eczema (treat with topical steroid + emollient)
DVT presentation Red, swollen, warm leg with deep aching pain; NO scaling or ring pattern; unilateral; Wells score criteria Not fungal or dermatological Rule out DVT — this is a vascular emergency requiring anticoagulation

Spreading cellulitis is a time-sensitive emergency

Redness that is expanding measurably every few hours, with fever, significant pain, and warmth out of proportion to any rash, is bacterial cellulitis until proven otherwise. Use a permanent marker to outline the redness border with date and time. If the redness crosses the line within 4–6 hours, the infection is spreading despite treatment — escalate immediately. A one-week delay starting antibiotics because "it might be fungal" can allow streptococcal cellulitis to progress to necrotizing fasciitis. For the full cellulitis and sepsis management framework, cross-link to wound infection recognition and treatment.

Treatment fundamentals: topicals, hygiene, and escalation

Topical regimen

The most common reason fungal infections relapse is stopping treatment early. The rash looks better at one week. It is not gone. The fungi are reduced, not eliminated. Stop at week one, and the infection returns within two weeks — often worse.

Standard rule: Apply antifungal cream twice daily (once daily for terbinafine) to the visible rash plus 1–2 cm (0.4–0.8 in) of surrounding normal-looking skin, and continue for the full prescribed duration.

Topical agent Coverage Typical dose Duration
Clotrimazole 1% cream Tinea (all types), Candida Twice daily 2–4 weeks
Terbinafine 1% cream Tinea (all types); NOT Candida Once daily 1 week (tinea pedis); 1–2 wks (other tinea)
Miconazole 2% cream Tinea, Candida Twice daily 2–4 weeks
Nystatin cream Candida ONLY — ineffective for tinea Twice daily 2–4 weeks

Sources: CDC Treatment of Ringworm; AAFP Intertrigo and Secondary Skin Infections 2014

Environmental hygiene

Antifungal cream clears skin; environmental hygiene prevents reinfection.

  • Wash towels, socks, underwear, and bedding at above 130°F (54°C). Fungi survive standard warm-water washes.
  • Bleach communal shower floors and bathroom surfaces weekly during active infections.
  • Do not share towels, washcloths, or footwear.
  • Treat footwear: apply antifungal powder inside shoes and boots, especially the toe box.
  • Keep separate towels per household member. Label them.

When to escalate to oral antifungal

Move from topical to oral when any of the following apply:

  • Tinea capitis — always. Topicals do not penetrate the hair shaft.
  • Onychomycosis with pain, diabetes, or functional limitation.
  • Widespread tinea (body surface area greater than one palm-width of involvement) not responding to 4 weeks of correctly-applied topical therapy.
  • Immunocompromised host — HIV, chemotherapy, corticosteroid-dependent. These patients need a lower threshold for oral therapy and closer monitoring.
  • Recurrent infection at the same site after completing full topical courses.

When to stop and reconsider the diagnosis

If a lesion that is being treated as fungal shows no improvement after 4 weeks of correctly applied topical antifungal, the diagnosis is likely wrong. Reassess against the differential in the previous section. Common substitutes at this point: nummular eczema, psoriasis, or contact dermatitis. A skin scraping with a potassium hydroxide preparation (KOH prep) at a clinic confirms or rules out fungal hyphae definitively — the only way to confirm the diagnosis in the field is the classic appearance plus treatment response.

Foot-care protocol for prolonged scenarios

Disabling athlete's foot stops you from walking, working, and evacuating. Foot care is not a comfort measure — it is a mission-critical task in any scenario involving extended foot travel or sustained wet conditions.

  1. Two pairs of boots in rotation. Air the off-pair overnight with insoles removed. Compressed foam and damp liner create a permanent fungal reservoir if never allowed to dry.
  2. Five to seven pairs of moisture-wicking socks. Wash and fully dry between wears. Wet socks worn the second day are a reliable mechanism for tinea pedis inoculation.
  3. Daily foot wash. Wash feet with soap and water. Dry thoroughly — spend extra time on the web spaces between toes, where moisture persists longest.
  4. Antifungal powder prophylaxis. In chronically wet conditions (flood response, winter operations, consecutive days in wet boots), dust antifungal powder (miconazole 2% or undecylenic acid) inside socks and boots each morning. This is prevention, not treatment — start before the rash appears.
  5. Cut toenails straight across. Avoid cutting the corners too short or rounding them. Ingrown nails create a portal of entry for bacterial infection directly in the tissue softened by fungal disease.
  6. Daily foot inspection. Remove boots and socks daily — at minimum before sleep. Look for: skin breaks, blisters, new patches of scaling, white maceration between toes, any warmth or swelling that does not resolve after boot removal.
  7. Severe wet conditions. In trench-foot-risk environments (days in standing water or non-waterproof footwear), change socks more frequently than once daily. Dry feet inside a sleeping bag at night when no other option exists. Trench foot and tinea pedis are distinct but often coexist — see field hygiene for the combined foot protocol.

Field note

The military's solution to athlete's foot is structural: two-boot rotation plus foot powder plus daily sock change. These aren't luxury habits — they're the difference between a functional operator at week six and one who cannot put weight on their feet. The foot powder tin is inexpensive and weighs almost nothing. Stock it alongside the antifungal cream.

Diabetics and the immunocompromised: escalate sooner

In a healthy person, fungal foot infections are an annoyance. In a diabetic, they are the first step in a cascade that ends in amputation. The path: tinea pedis → skin barrier breakdown → bacterial superinfection → cellulitis → foot ulcer → osteomyelitis → amputation. Every step in that chain is preventable with early intervention.

Mandatory practices for diabetics and immunocompromised individuals:

  • Daily foot inspection without exception. Any new redness, warmth, blister, or skin break in a diabetic foot is an emergency until proven otherwise.
  • Antifungal at first sign. Do not wait for a classic scaly ring to appear — treat any erythema in the interdigital web spaces immediately.
  • Lower threshold for oral therapy. Topicals are first line, but any diabetic with tinea pedis that does not respond within 2 weeks warrants oral terbinafine consideration.
  • Any non-healing lesion in a diabetic foot requires bacterial wound assessment per wound infection recognition — fungal and bacterial infections commonly coexist in diabetic feet.
  • Onychomycosis in diabetics is not cosmetic. Thickened, crumbling nails cut the surrounding skin during normal gait and create bacterial entry points. Treat it.

For the full chronic-conditions framework in emergency scenarios, see chronic conditions in emergencies.

Common mistakes that get people sidelined

Treating bacterial cellulitis as fungus. Red, spreading, warm skin after a scratch or bite is cellulitis until proven otherwise. The telltale signs that exclude simple fungus: no scaly border or central clearing, rapidly expanding redness measurable hour to hour, fever, systemic symptoms. Starting antifungal cream on cellulitis while the infection spreads toward a lymph node is a potentially fatal delay. Cross-reference wound infection if any doubt exists.

Treating fungus as cellulitis. Unnecessary antibiotic courses gut the microbiome, increase C. difficile risk, and fail to clear the fungal infection. The ring with a scaly border, central clearing, and absent fever indicates fungus; antifungal cream clears it in two to four weeks.

Stopping topical therapy when "it looks better." The itch resolves in the first week. The organism is not gone. Stopping at week one produces a two-week relapse almost universally. Complete the full course.

Sharing the cream tube. Rolling the same tube between household members cross-contaminates everyone. Each person needs their own supply.

Applying cream to wet skin. Drug absorption drops significantly on macerated or wet skin. Dry the area fully before applying.

Wearing the same wet boots day after day. The boot becomes a fungal reservoir with effectively infinite spore pressure on the skin. No topical can overcome daily re-inoculation from inside the boot. Boot rotation is not optional.

Cutting toenails incorrectly. Rounding the corners produces ingrown nails. Ingrown nails in a fungal-softened nail bed become infected. That bacterial wound in a diabetic is how amputations happen.

Treating scalp tinea in a child as severe dandruff. Dandruff is a different condition entirely (seborrheic dermatitis). Tinea capitis causes hair loss — dandruff does not. Selenium sulfide shampoo alone will not cure tinea capitis. A child with scaly scalp and patchy hair loss needs oral antifungal therapy, not medicated shampoo as the sole treatment.

Teach your family

When professional medical care is unavailable for weeks, these six rules replace the clinic visit for managing fungal infections:

  1. Dry feet completely after every wash. Dry between each toe with a clean towel. Moisture is the substrate fungi grow in — control it.
  2. Use the cream twice daily for the full 2–4 weeks, not just until the itching stops. The itch goes away before the organism does.
  3. If there is a ring with a scaly border and it is itchy, it is probably fungus — start cream and finish the course.
  4. If the redness is spreading fast, hot, and painful, and the person has a fever — this is not fungus. It is probably bacterial cellulitis. Start antibiotics per wound infection and accelerate evacuation if antibiotics are not available.
  5. Do not share towels, socks, or the cream tube. Towels share fungal spores. One infected household member can reinfect everyone who shares a towel.
  6. Wash towels and bedding hot — above 130°F (54°C) — at least once a week while anyone in the household has active tinea.

The pages most relevant to fungal skin management in austere settings:

  • Pathogens: germs, infection types, and field decisions — the foundational framework covering what antifungals do, what they don't do, and how to apply the pathogen-class mental model to treatment decisions
  • Wound infection recognition and treatment — full bacterial cellulitis management, STONES assessment, sepsis recognition, and qSOFA criteria when a rash stops looking like a rash
  • Field hygiene for disease prevention — foot care protocol, group hygiene in shelter, towel separation, and preventing fungal transmission in shared living situations
  • Wound care — management of skin breaks that arise from macerated fungal skin, ingrown nails, or bacterial superinfection
  • Tick bite management — erythema migrans identification and doxycycline prophylaxis criteria for the Lyme rash that mimics ringworm
  • Chronic conditions in emergencies — diabetic foot care framework and the escalation posture for immunocompromised household members
  • Medical supply stockpiling — antifungal quantities, shelf life, and storage guidance for clotrimazole, terbinafine, and nystatin in a 30–90-day stockpile

Sources and next steps

Last reviewed: 2026-05-22

Source hierarchy:

  1. CDC Treatment of Ringworm (Tier 1, CDC Fungal Diseases program — topical antifungal duration and agent selection)
  2. AAFP — Intertrigo and Secondary Skin Infections (Tier 1/2, peer-reviewed AAFP clinical review — candida intertrigo diagnosis and treatment)
  3. FDA Lamisil Oral Granules (terbinafine) label (Tier 1, FDA prescribing information — weight-band dosing 125 / 187.5 / 250 mg × 6 weeks for pediatric tinea capitis ≥4 years)
  4. PMC — Management of Tinea Capitis in Childhood (Tier 1, NIH PMC peer-reviewed — pediatric oral antifungal context)
  5. AAFP — Common Tinea Infections in Children (Tier 1/2, peer-reviewed AAFP — griseofulvin dosing and species-specific selection)
  6. Gupta 2012 — Evidence-based optimal fluconazole dosing for onychomycosis (Tier 1, peer-reviewed clinical research — once-weekly pulse fluconazole regimen)

Legal/regional caveats: Oral antifungals (terbinafine, griseofulvin, fluconazole) require a prescription in the United States and most countries. This page describes treatment rationale for extended-disruption scenarios where professional medical care is unavailable. Topical agents (clotrimazole, miconazole, terbinafine 1% cream) are over-the-counter in the US and require no prescription. Scope of practice varies by jurisdiction.

Safety stakes: high-criticality topic — recommended to verify thresholds before acting, particularly for pediatric oral antifungal dosing and any case where bacterial cellulitis cannot be confidently excluded.

Next 3 links: