Cold Sores and Inner Lip Location
Cold sores (herpes labialis) caused by HSV-1 typically occur on the outer lips and perioral skin, NOT on the inner lip (oral mucosa). 1, 2
Anatomical Distribution of HSV-1 Infections
Cold sores characteristically present as recurrent vesicular eruptions primarily on the lips and perioral skin—the outer vermilion border and surrounding facial skin. 2 The inner lip (oral mucosa) is not the typical location for herpes labialis. 1
Key Distinguishing Features:
Herpes labialis (cold sores): Affects the outer lip, vermilion border, and perioral skin with grouped vesicles that progress through stages of papule, vesicle, pustulation, ulceration, and scabbing 1
Primary herpetic gingivostomatitis: When HSV-1 affects the oral cavity (including inner lip/oral mucosa), it typically presents as acute primary infection with fever and widespread oral ulcerations, not as recurrent "cold sores" 3, 4
Clinical Implications
If you observe vesicular or ulcerative lesions on the inner lip mucosa, consider alternative diagnoses:
Primary herpetic gingivostomatitis (first HSV infection): Presents with fever, widespread oral ulcerations affecting gingiva, tongue, and oral mucosa—this is a different clinical entity than recurrent cold sores 3, 4
Aphthous ulcers (canker sores): These occur on the inner lip and oral mucosa but are NOT caused by herpes simplex virus 4
Other conditions: Kawasaki disease specifically notes that oral ulcerations are NOT seen in their diagnostic criteria, helping distinguish from HSV 5
Important Clinical Pitfall
Do not confuse recurrent herpes labialis (cold sores on outer lips) with primary herpetic gingivostomatitis (which can affect inner oral mucosa). 3 These are distinct clinical presentations of HSV-1 infection:
- Recurrent cold sores = outer lip, localized, mild 1, 2
- Primary gingivostomatitis = inner mouth, widespread, severe with fever 3, 4
In immunocompromised patients, HSV lesions may extend beyond typical locations and involve the oral cavity or extend across the face, but this represents severe, atypical disease rather than typical cold sores. 1