Herpes Simplex (Cold Sores / Oral & Facial HSV) ICD-10: B00.9

Viral skin infection / Infectious disease

Often searched as: cold sore on lip, blisters on mouth, lip blister that comes back, fever blister, tingling before cold sore, HSV cold sore treatment, cold sore how long does it last, herpes simplex photos…

Clinical urgency level

lowmediumhigh

Systems Affected

skinoral and labial mucosaeyes (herpetic keratitis)central nervous system (rare — herpes encephalitis)neonatal (serious complication in newborns)

Severity Levels

mild

Recurrent labial herpes (cold sores) — small cluster of blisters on the lip, self-limiting in 7–10 days, manageable with topical or episodic oral antivirals.

moderate

Primary oral HSV with widespread intraoral ulcers, fever, and difficulty eating; or herpetic whitlow (finger infection); or frequent recurrences (6+/year) requiring suppressive therapy.

severe

Eczema herpeticum (HSV spreading across eczematous skin — emergency), herpetic keratitis (eye involvement — risk of blindness), herpes encephalitis, or neonatal herpes — all require urgent hospitalization.

Red Flags

Eye redness, pain, or blurred vision during an HSV outbreak (herpetic keratitis — risk of blindness)
HSV outbreak in a person with atopic dermatitis that is spreading rapidly across the skin (eczema herpeticum — emergency)
Severe headache, confusion, or neck stiffness alongside an HSV outbreak (herpes encephalitis)
Newborn exposure to active maternal herpes at delivery
Very frequent recurrences (more than 6/year) in an otherwise healthy adult — consider HIV testing
HSV outbreak in an immunocompromised person with slow healing or spreading lesions

Clinical Presentation

Herpes simplex labialis — grouped vesicles on the vermillion border of the lip

Source: Wikimedia Commons (CC BY-SA 3.0 )

Herpes simplex image gallery — DermNet NZ

View gallery on DermNet NZ (image gallery reference)

When to See a Doctor

See a doctor immediately for eye involvement, rapidly spreading skin blisters in an eczema patient, or neurological symptoms. For typical cold sores, antiviral treatment within 48–72 hours of the first tingle shortens duration. People with frequent outbreaks (6+/year) benefit from daily suppressive antiviral therapy — discuss with a doctor.

Differential Diagnosis

Impetigo (honey-crusted — bacterial, no prodrome, responds to antibiotics)
Aphthous ulcers (canker sores — inside the mouth, no blisters, not viral)
Hand, foot and mouth disease (HFMD — Coxsackievirus, affects palms/soles/mouth, mainly in children)
Varicella (chickenpox — widespread, not grouped, different distribution)
Herpes zoster (shingles — dermatomal, unilateral, in adults)
Fixed drug eruption (recurring in same location after medication)

Comorbidities

Atopic dermatitis (major risk factor for eczema herpeticum)
HIV / immunosuppression (severe, frequent, treatment-resistant outbreaks)
Herpetic keratitis (recurrent eye disease — leading infectious cause of corneal blindness)
Aseptic meningitis (rare complication)
Erythema multiforme (recurrent HSV is the most common trigger)

Prognosis

Herpes simplex is a lifelong infection — the virus cannot be eliminated. Cold sores recur in ~30–40% of infected individuals, typically becoming less frequent over time. Oral antivirals (acyclovir, valacyclovir) shorten outbreaks and, taken daily, reduce recurrence by 70–80%. Eczema herpeticum and herpetic keratitis require urgent treatment to prevent serious complications. Herpes encephalitis, while rare, carries significant mortality without prompt IV acyclovir treatment.

Detailed Overview

Causes, Symptoms, and When to Take Action Herpes simplex is a common viral infection that manifests as recurrent vesicular lesions on the skin or mucous membranes. It is caused by HSV-1 or HSV-2 and can affect different body regions depending on the virus type. How It Looks Texture: Clusters of small, fluid-filled vesicles on a red, inflamed base Color: Red base with clear or yellowish vesicles Shape: Grouped vesicles that eventually ulcerate and form crusts Location: Commonly occurs on the lips (cold sores), mouth, or genitals; can also affect fingers (herpetic whitlow) Why Does It Appear? Herpes simplex infects skin or mucous membranes through contact with an active lesion. Primary infections tend to be more severe. Recurrent infections are usually milder and shorter. In immunocompromised individuals, infections may be more extensive and frequent. Should You Be Concerned? Herpes simplex is usually not dangerous but can cause discomfort. Unusually widespread, persistent, or severe lesions — especially in individuals with weakened immunity — warrant professional evaluation. Can You Prevent It? Avoid contact with active lesions and recognize warning signs early to minimize spread. 👉 How Piel AI Can Help Piel AI lets you track skin and mucosal lesions over time using photos to help notice patterns or changes. Summary Herpes simplex causes recurring vesicular lesions, often on lips or genitals. Primary outbreaks are more severe; recurrences tend to be milder. Though usually benign, it can be problematic in vulnerable individuals. Monitoring and early recognition help manage flare-ups and transmission.

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