Healthy Foot Skin
Intact stratum corneum, dry interdigital spaces, no pathogens present.
- ~5.0: Interdigital pH (acid mantle intact)
- Low: Skin moisture (dry toe web)
- 0%: Fungal burden (no colonization)
- 100%: Barrier integrity (unbroken stratum corneum)
Foot skin anatomy
Thick stratum corneum, thin web spaces, keratin barrier.
Normal microflora
Resident bacteria and yeast, low-level, non-pathogenic.
Barrier defenses
Acid mantle, sebum, desquamation limit colonization.
Dermatophyte Exposure
Warm, moist shared surfaces transfer spores to interdigital skin.
- Locker rooms: Common source (shared showers, mats)
- T. rubrum: Primary organism (most frequent species)
- ~12%: Fungal burden (early colonization)
- 1–3 wks: Incubation (to visible symptoms)
Spore transmission
Arthrospores survive on damp floors for weeks.
Risk environment
Occlusive shoes, sweat, warmth favor colonization.
Interdigital preference
4th web space is narrowest, most humid site.
Fungal Growth & Symptoms
Hyphae invade keratin, producing scale, itch, and maceration.
- ~68%: Fungal burden (progressing infection)
- Itch: Symptom onset (plus scaling, fissuring)
- Macerated: Web space (white, softened skin)
- Active: Keratinase (digests keratin for nutrients)
Hyphal invasion
Branching filaments spread laterally through keratin.
Inflammatory response
Itching, erythema, and fissuring develop.
Maceration risk
Moisture trapping softens skin, aids penetration.
Topical Antifungal Applied
Terbinafine kills hyphae directly; clotrimazole halts their growth.
- Fungicidal: Terbinafine (kills fungal cells)
- Fungistatic: Clotrimazole (halts fungal growth)
- Ergosterol: Mechanism (membrane synthesis blocked)
- ~86%: Peak burden (at treatment start)
Terbinafine mechanism
Blocks squalene epoxidase, ruptures fungal membrane.
Clotrimazole mechanism
Blocks ergosterol synthesis, stalls fungal growth.
Application routine
Applied to clean, dry interdigital skin daily.
Clearance Over the Treatment Course
Fungal burden declines; terbinafine clears faster than clotrimazole.
- 1–2 wks: Terbinafine course (typical clearance)
- ~4 wks: Clotrimazole course (needs longer course)
- <1%: Terbinafine day 14 (burden remaining)
- ~26%: Clotrimazole day 14 (burden remaining)
Fungicidal clearance
Rapid hyphal death, short course, low relapse.
Fungistatic clearance
Slow immune-driven clearance, longer course needed.
Immune dependence
Clotrimazole relies on intact host immune clearance.