ICD-10 Code B09 – Unspecified viral infection characterized by skin and mucous membrane lesions (2026): Diagnosis, Symptoms & Billing Guide
2026 ICD-10-CM Diagnosis Code B09 – Unspecified viral infection characterized by skin and mucous membrane lesions
What it is
B09 is used for a viral illness that causes skin and mucous membrane lesions but is not identified as a specific viral disease. Use it when the record documents a nonspecific viral exanthem or similar presentation without a named cause.
Clinical signs
Typical findings include a rash, mucosal lesions, or both, with the exact appearance depending on the underlying virus. Clinical features vary; refer to documentation.
When to use this code
Use B09 when the clinician documents an unspecified viral infection with skin or mucous membrane involvement and does not name a more specific diagnosis. It also fits when the note describes a viral rash or exanthem but the organism is not identified. If the chart later specifies a distinct viral condition, code that diagnosis instead.
Do not use for
Do not assign B09 when the record supports a specific viral disease with its own ICD-10-CM code. Do not use it for nonviral rashes or lesions; check documentation.
Coding tip
Query for the exact viral diagnosis before defaulting to B09, because a more specific code may be available.