Harvard Men's Health Watch

Preventing cold sores

Ask the doctor

Q. What's the fastest way to get rid of a cold sore? Is it possible to prevent them?

A. Cold sores, also called fever blisters, are bothersome and painful fluid-filled blisters on or around the lips. They are caused by infection with herpes simplex virus (usually type 1). Cold sores heal on their own in seven to 10 days. However, antiviral medications can modestly shorten the healing period. One-day treatment with the prescription antiviral drugs famciclovir (Famvir) or valacyclovir (Valtrex) shortens cold sore symptoms by one to two days. These oral medications are most effective when taken at the first sign of a cold sore, such as a burning or tingling sensation. Antiviral creams are less effective and need to be applied several times daily for five days.

To prevent cold sores, valacyclovir or another antiviral drug, acyclovir (Zovirax), can be taken daily. This reduces the chance of a cold sore coming back by about one-third. It could also help if you avoid triggers, such as exposure to sun or wind, that can activate the cold sore virus. If sun exposure is a trigger for you, using sunscreens can help. You may have heard that the amino acid lysine, taken as a dietary supplement, can prevent cold sores, but the evidence for this is not very good.