Cold sores are gross. They're painful and puss-filled (which means they're also potentially explosive), unsightly and contagious, and they become even worse when you start throwing out causes like "the herpes simplex virus." Yes. Herpes. On your lips.
Herpes does actually get around quite a lot. Besides its infamy as an STD, other forms of the virus masquerade as friendly things like chickenpox and shingles (Herpes Zoster) and always causes itchy or painful fever blisters, rashes, and plenty of annoyance and discomfort.
(Isn't there just something about herpes being on your lips though?)
Cold sores (or fever blisters) are actually little blisters that usually come in groups - little clusters of joy that form on the lips and around the mouth. They're contagious, and the virus can be passed when a person touches a cold sore or an infected object, which means that kissing, sharing bathroom items or eating utensils, and touching the saliva of a cold sore sufferer are all great ways to pick up the virus. (If you're married to someone who gets cold sores and you come into some kind of regular contact with each others' saliva, you're doomed. Get used to it.)
Some people just get small outbreaks, while others have really painful cold sores. They usually start with some pain around the mouth, but sometimes the symptoms include fever, sore throat, and swollen glands. (And drool, but only if you're a small child.)
The best way to avoid getting cold sores is to avoid contact with cold sore sufferers' saliva. If you already have the virus, you can avoid outbreaks by:

  1. Avoiding stress situations
  2. Staying healthy (colds and flu tend to trigger cold sores, which is probably where they got their name)
  3. Washing your hands often during outbreaks and avoiding touching the sore as often as possible
  4. If you get cold sores often or the outbreaks get too severe, talk to a doctor about some prescription medication options.
Once you have an outbreak, you have two options. First, they will heal on their own eventually. They break open, leak out, crust over and then finally heal. (Tasty, huh?) This can take several days to two weeks. Other options include using medications like Abreva or other skin cremes and ointments. In most cases they will only speed up the healing process by a couple of days, but they can ease the pain associated with cold sores, and they can start the healing process faster if the blisters are embarrassing. Since cold sores usually keep coming back, it isn't a bad idea to invest in some kind of healing cream to make outbreaks less miserable.
Now go and wash your hands, please.