Skin Mycosis (Fungal Skin Infection) ICD-10: B36.9

Fungal / Infectious skin condition

Often searched as: ringworm on skin, fungal rash that won't go away, itchy circular rash, athlete's foot, fungal infection between toes, yellow thick toenails, scaly patch on skin, rash in skin folds…

Clinical urgency level

lowmediumhigh

Systems Affected

skinnailsscalpmucous membranes

Severity Levels

mild

Localized superficial fungal infection (e.g., athlete's foot, ringworm) responding to over-the-counter antifungal treatment within 2–4 weeks.

moderate

Persistent or recurrent infection, nail involvement (onychomycosis), or spread to multiple body areas — requires prescription antifungals.

severe

Deep or systemic fungal infection, especially in immunocompromised individuals — can be life-threatening and requires urgent specialist care.

Red Flags

Infection not improving after 2–4 weeks of antifungal treatment
Rapidly spreading rash or new patches appearing
Significant nail destruction (thickening, crumbling, separation from nail bed)
Scalp infection with hair loss or boggy, swollen areas (kerion — medical emergency in children)
Fungal infection in an immunocompromised person (HIV, chemotherapy, diabetes) — can spread internally
Rash accompanied by fever or spreading redness beyond the lesion borders

Clinical Presentation

Tinea corporis (ringworm) — classic circular scaly rash on the arm

Source: Wikimedia Commons (CC BY-SA 3.0 )

Onychomycosis — nail fungal infection with thickening and discoloration

Source: Wikimedia Commons (CC BY-SA 3.0 )

When to See a Doctor

See a doctor if a rash that looks like ringworm doesn't improve with over-the-counter antifungal cream after 2 weeks, if nails are thickening or crumbling, or if the infection is on the scalp (especially in children). People with diabetes or weakened immune systems should always see a doctor for any fungal infection.

Differential Diagnosis

Psoriasis (scaly plaques — can mimic tinea)
Eczema / atopic dermatitis
Contact dermatitis
Pityriasis rosea
Seborrheic dermatitis
Nummular eczema (coin-shaped patches)
Inverse psoriasis (in skin folds)

Comorbidities

Diabetes mellitus (major risk factor — glucose-rich environment favors fungi)
HIV / AIDS and other immunodeficiencies
Obesity (skin folds create warm, moist environments)
Hyperhidrosis (excessive sweating)
Antibiotic or corticosteroid use (disrupts normal skin flora)

Prognosis

Most superficial fungal infections respond well to topical antifungals within 2–4 weeks. Nail fungus (onychomycosis) is the most stubborn — oral antifungals (terbinafine) over 3–6 months achieve cure in 70–80% of cases, but recurrence is common. Recurrent or treatment-resistant infections should prompt evaluation for underlying conditions like diabetes or immune suppression. In immunocompetent individuals, prognosis is excellent with appropriate treatment.

Detailed Overview

Causes, Symptoms, and When to Take Action Skin mycosis refers to fungal infections of the skin, nails, hair, or mucous membranes. These infections are common and usually not dangerous, but they can cause discomfort and cosmetic concerns. How It Looks Texture: Red, scaly, or bumpy rashes; sometimes thickened or flaky skin Color: Red or pink on lighter skin; darker, brown, or gray on more pigmented skin Shape: Circular or irregular patches, sometimes with a clearer center and more active border Location: Often in skin folds, feet, nails, scalp, or areas exposed to warmth and moisture Why Does It Appear? Skin mycoses are caused by fungi that overgrow under favorable conditions. Contributing factors include: Warm and humid environments Excessive sweating Breaks in the skin barrier (cuts, scratches) Weakened immune system or chronic illnesses Should You Be Concerned? Most fungal infections are mild, but medical evaluation may be needed if: Lesions spread, worsen, or do not improve Nails become thick, brittle, or painful You experience recurrent infections You have an underlying condition that weakens immunity Can You Prevent It? Keep skin and nails clean and dry Avoid sharing personal items such as towels, shoes, or nail tools Wear breathable clothing and shoes to reduce moisture Pay attention to small skin injuries to prevent fungal entry 👉 How Piel AI Can Help Piel AI can help you monitor skin changes over time using regular imaging. While not diagnostic, it allows you to track the spread or improvement of lesions and provides useful information to discuss with a healthcare provider. Summary Skin mycosis is a fungal infection that can affect skin, nails, and mucous membranes. It presents as discolored, scaly, or itchy patches. Risk factors include humidity, skin injury, and weakened immunity. Good hygiene and monitoring help reduce risk and manage recurrence.

Explore more conditions

Learn about other skin and hair conditions.

View all conditions →