Cold-sores are caused by the herpes simplex virus (HSV ). Usually they are caused by HSV-1. (While genital herpes is usually caused by HSV-2). HSV infection and cold-sores are an incredibly common problem. By age fifty, 90% of people will test positive for antibodies to HSV-1 meaning that they have either been infected or at least exposed to this virus. However, only about one third of those people will develop the clinical lesions that we call “cold-sores”. Some studies show that as many as 40% of the general population have experienced at least one cold-sore.
Why Is It Called a “Cold Sore”?
Because it comes out when you have a “cold”. The same reason some people call it a “fever blister”. The HSV virus, which is always present in your body, tends to overcome the immune system and erupt as blisters that turn into “sores” when your immune defenses are run down. This is especially common during a “cold” or a “fever” or after a sunburn. And sometimes it comes out for no reason at all.
How Do You Catch Oral HSV?
Most people will have contracted the virus as a child. The method of infection is contact with infected material such as saliva (e.g. a kiss from a relative who gets cold-sores or sharing a drink with a friend who gets cold sores). Patients who get cold-sores continue to shed the virus in their saliva even when the cold-sore is no longer visible.
Treating Cold Sores: A “Window of Opportunity”
As a general rule, herpes infections must be treated early or the therapy will not be effective. This is because viral replication is most active during this early period. Most patients with herpes labialis describe a “prodrome”. That means that they are able to feel the cold sore (with symptoms such as burning or tingling) before they can actually see the sore.
Topical Therapy (Creams)
Here is a case where the over-the-counter product may be superior to the prescription products. Abreva (docosanol 10% cream) is sold without a prescription and should be used at the first sign of a cold-sore 5X/day. The prescription creams available to treat cold sores include Denavir cream and Zovirax cream or ointment. Some studies argue that prescription Denavir is the most effective topical mediation for cold-sores, others argue that Abreva is superior. Either way, the average effect for these medicines is to decrease the cold sore outbreak by 12 to 24 hours. So if it was going to last five days, now it will last four days or four and a half days. Oral medicines work better…
Oral Therapy (Pills)
All oral therapies for the HSV virus are available only with a prescription. In the last few years, easy one-day dosing has become available. The two brands are Valtrex and Famvir and the dose is high, but it is only taken for one day. It is important that the medication be started at the first symptom (the first “tingle”) of a cold-sore. Preferably, before you can see a blister. I tell patients to take it if you even think you are going to get a cold-sore. If you wait until you are sure that you are getting a cold-sore, it could be too late for the medicine to have a significant effect.