Cold Sores (Herpes Simplex) — Ireland Patient Guide

What causes cold sores

Cold sores are caused by Herpes Simplex Virus (HSV), most commonly HSV-1. After first infection (often in childhood) the virus stays dormant in nerves and can reactivate during stress, illness, or UV exposure.

Stages of a cold sore

1. Tingling — start antiviral here for best effect
2. Small fluid-filled blisters (most contagious phase)
3. Weeping then crusting
4. Healing — usually 7–10 days total

When antivirals help

Topical aciclovir cream is widely available without prescription. Oral aciclovir or valaciclovir (prescription) is more effective, particularly for: severe outbreaks, frequent recurrences (more than 6 per year — consider suppression), first-ever outbreak, and immunocompromised people.

Avoiding spread

• Do not share lip products, towels, or razors during an outbreak
• Avoid kissing infants, immunocompromised people, or people with eczema during outbreaks (eczema herpeticum risk)
• Wash hands after touching the area

When to consult online

Recurrent cold sores, severe first outbreaks, or any spreading rash beyond the lip border. If you notice eye involvement (red, painful eye with cold sore), seek same-day in-person eye assessment.

FAQs