What Causes Oral Cold Sores?
Cold sores are caused by the herpes simplex virus, most commonly the type 1 strain, although the type 2 strain normally responsible for genital herpes is also capable of causing them but that's generally very rare. The herpes virus currently has no known cure and once you've been infected you've got it for life – this is because when the virus is dormant it retreats into a sort of hibernation mode inside the nerve cells near the site of the initial infection.
The herpes virus cycles in periods of active and dormant stages, with the dormant stage being predominant – this is the stage that the virus is in when you do not have a visible cold sore. The active stage is when an outbreak occurs and you get a cold sore (or some, as the case may be), which will usually last between 2 and 21 days, with about a week being average for most people.
How Did You Get Infected?
Studies have shown that the most likely initial source of infection when you acquired the herpes simplex virus that causes your cold sores was being kissed by a close relative as a child who had a cold sore at the time. So yes, you can likely thank grandma for your life-long herpes infestation.
What You Think Is A Cold Sore Might Not Be!
Many people confuse cold sores and canker sores – they are not the same thing! Cold sores are caused by a virus, whereas canker sores, aka "aphthous ulcers", are caused by bacterial infections. Cold sores can never be gotten rid of (because you can not ever eliminate the virus from your system), whereas canker sores can be treated with anti-biotics and the bacteria will be quickly eliminated and the canker sores along with them.
The easiest way to distinguish a canker sor from a cold sore is this: cold sores almost always occur outside the mouth, whereas canker sores are always inside the mouth, usually in a soft tissue area like the inside of the lip. They also look different, the most obvious difference being the cold sores are red, from beginning to end when they crust over, whereas canker sores are typically of a whitish color.