Cold sores most commonly appear on the lips and immediately around the mouth. They are a symptom of infection by the herpes simplex virus, typically HSV-1 (that's the type 1 strain of the virus, as opposed to HSV-2, the type 2 strain usually responsible for genital herpes), and once the virus has infected someone it will remain inside the sensory nerve cells near the initial site of infection (usually the face, more specifically the lips) for the rest of their life. Currently, there is no cure, although vaccines against the herpes simplex virus are in the works.

Herpes simplex cycles between active periods (when you've actually got a cold sore you can see) of about 2-21 days and dormant periods when the virus simply retreats to the safety of the nerve cells and does nothing. Mind you, however, that just because you're not showing any symptoms, such as a cold sore, does not mean that you're not contagious. You could be undergoing what's known as asymptomatic shedding (asymptomatic means you don't have any symptoms), which almost always occurs up to a week before and after an active outbreak, so if you're about to get a cold sore or you just had one, you're probably still contagious and capable of spreading the virus to other people.

Cold Sore Prevention

One of the best, and proven, ways to prevent cold sores is by taking lysine as a supplement. It's been shown in multiple scientific studies that 500mg of lysine once a day significantly reduces the number of outbreaks suffered over a one year period versus the control group that didn't take any lysine.

Also, you should remember that Vitamin C does an excellent job of boosting your immune system, so you should be taking it regardless, but it's known that whenever a cold sore outbreak occurs it almost always coincides with a period of decreased immune function (other illness, cold weather, stress, immunosuppressive drugs, etc.).

Cold Sore Triggers

It's been shown that there are a number of predictable circumstances that will tend to trigger an outbreak over and over again. The most common of these is STRESS, which can sometimes be a secondary product of another illness which weakens your immune system anyway and then the byproduct of dealing with the illness, perhaps because you have to work or take care of your kids regardless of the fact that your sick, drops your immune system even further thereby increasing the odds of getting a cold sore even more, and when that cold sore does come it will tend to be worse and last longer because your immune system can't deal with the herpes virus as effectively as it normally can.

An Odd Thing About Herpes

The odd thing is that contracting herpes causes an immune response called seroconversion from the body which releases antibodies to that specific strain of HSV which will thereby prevent an infection by that strain at any other site in the body--if you get oral herpes that means you are now immune to and cannot get herpes whitlow, herpes keratitis, or herpes encephalitis. It's also been shown that exposure to HSV-1 (i.e. in the form of oral herpes) seems to reduce the symptoms of a later HSV-2 infection (i.e. genital herpes), and most indications are that an HSV-2 infection will immunize that person against HSV-1, so if you get genital herpes odds are very good that you're now immune to and cannot get oral herpes. I'm not sure how much of a "good" thing this is supposed to be, but perhaps it's a silver lining in every cloud sort of thing?