ICD-10 Code B35.1 – Tinea unguium (2026): Diagnosis, Symptoms & Billing Guide
2026 ICD-10-CM Diagnosis Code B35.1 – Tinea unguium
What it is
B35.1 identifies a fungal infection of the nails, most often affecting toenails. It is used when documentation states tinea unguium or onychomycosis caused by dermatophytes.
Clinical signs
Typical findings include nail discoloration, thickening, brittleness, and subungual debris. Clinical features vary; refer to documentation if the record does not clearly describe fungal nail disease.
When to use this code
Use B35.1 when the provider documents tinea unguium, fungal nail infection, or dermatophyte infection of the nail. Code it when the affected nail is identified and the diagnosis is established in the note. If the chart only mentions nail changes without a fungal diagnosis, check documentation.
Do not use for
Do not use this code for nonfungal nail disorders such as trauma-related nail dystrophy or psoriasis. If the condition is unspecified or another fungal site is documented, choose the code that matches the record.
Coding tip
Confirm that the provider links the nail finding to a fungal infection before assigning B35.1.