Cold sores

• primary oral infection with the herpes simplex virus (HSV)
  • typically occurs at a young age
  • is asymptomatic
• after primary oral infection, HSV may persist in a latent state in the trigeminal ganglion
  • it may later reactivate as the more common herpes labialis, or "cold sores." (1)
• these are recurrent herpes simplex infection around the mouth.
• these lesions have a variable recurrence rate and may be associated with respiratory infections.
• their occurence may be also related to non-specific factors such as:
  • emotional stress
  • menstruation
  • sunshine
• the classical manifestation is a well-localized cluster of small vesicles along the vermilion border of the lip or adjacent skin
  • the vesicles rupture, ulcerate, and crust within 24 to 48 hours
  • they spontaneously heal over seven to 10 days

Public Health England guidance states (2):

• most resolve after 5 days without treatment
• topical antivirals applied prodromally can reduce duration by 12 to 18 hours
• if frequent, severe, and predictable triggers:
  • consider oral prophylaxis: aciclovir 400mg, twice daily, for 5 to 7 days

Comprehensive Cochrane systematic review evaluating 87 RCTs (22,631 immunocompetent participants) across 58 topical, oral, and physical interventions for treating herpes labialis (cold sores) (3):

• topical antiviral efficacy: topical nucleoside antivirals (aciclovir and penciclovir creams) speed up cold sore healing time by approximately 1 day compared with placebo; head-to-head comparison shows similar efficacy between aciclovir and penciclovir creams
• oral antiviral efficacy: oral valaciclovir reduces cold sore healing time by approximately 1 day compared with placebo, whereas oral aciclovir demonstrated little to no significant difference in healing time
• safety and adverse events: severe adverse events are rare across all antiviral modalities, and mild-to-moderate adverse events are uncommon and balanced between active treatment and placebo groups

Reference:

• (1) Wanda C. Gonsalves .Common Oral Lesions: Part I. Superficial Mucosal Lesions. Am Fam Physician 2007;75:501-7.
• (2) Public Health England (June 2021). Managing common infections: guidance for primary care
• (3) Lin HS, Lin PT, Shih IC, Lu ML, Tsai YS, Chi CC. Interventions for treatment of herpes labialis (cold sores on the lips). Cochrane Database of Systematic Reviews. 2026, Issue 9. Art. No.: CD015216.