Harvard Women's Health Watch

By the way, doctor: Does lysine prevent cold sores?

Q. For years, I was plagued by cold sores and took antiviral drugs to treat the outbreaks. But at a friend's suggestion, I started taking lysine every day, and it seems to prevent them altogether. What do you know about this supplement?

A. Cold sores (sometimes called fever blisters) are painful fluid-filled lesions on or near the lips that are caused by the herpes simplex virus (HSV). There are two kinds of HSV: HSV-1, which causes most cold sores, and HSV-2, which is mostly responsible for genital herpes. HSV-1 infection is very common and easily transmitted by kissing or other contact with saliva. Once you're infected, the virus lays dormant in the nerve cells that supply sensation to the skin. When the virus becomes active, it travels to the skin surface and multiplies, causing an outbreak.

Oral antiviral drugs (acyclovir, valacyclovir, and famciclovir) are used to treat both cold sores and genital herpes. Taken at the first inkling of a cold sore, they can help shorten the duration of symptoms. So can topical acyclovir and penciclovir.

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