I think one of the main ones is stress. lol

The Herpes Simplex virus.

Kissing someone with a dirty mouth...maybe?

I believe it is simply some kind of benign virus that some people are prone to get..my mom always got cold sores..I used to get canker sores. Some people get yeast infections. Happy Wednesday! :) ((hugs))

Stop living a life of sin and laying with people out of wedlock and you won't get them anymore! abstenance is the key!! it's as easy as that people! - Donnie "GodROCKS" Glax

Rundowness

The sun kills the bacteria around the lips that controls the Herpes I virus that causes cold sores. I'm an expert on this.

yes- ice inhibits them but hurts surrounding tissue- I use a mixture of Neosporin and makeup to hide the blemish after the blister stage (I use a pin to pop the blisters)- best defense is good health, a bland diet, no cholcolate or coffee, no stress, a little vitamin C, and hope the weather doesn't change too rapidly

Change in weather, sunburn, wind or stress, that's usually when I get a cold sore...

herpes virus

herpes virus also they come more often if you are sick or stressed

From: http://ezinearticles.com/?Tell-Me-What-Causes-Cold-Sores&id=585332 Everyone is different and each cold sore event unique. But for the vast majority of us cold sore victims, what causes cold sores is quite similar. First, let us not forget that the root cause of all cold sores is the herpes simplex virus. There are eight known types of herpes, two of which have been identified as causing cold sores. These are herpes simplex type 1 or type 2. Nearly everyone in the world carries these highly contagious viruses. Normally, this virus is dormant. Should it become active, it will begin the replication process on your lip or nose. This is basically what causes all cold sores. The key, then, to learning what causes cold sores is actually to determine what the triggers are that causes the your cold sore virus to wake up. Stress is claimed to be the main trigger for causing cold sores to break out. Most common stress triggers that create cold sores are illnesses or injuries. Cold sores often occur during a bout with the cold or flu virus. The cold and flu season is also the cold sore season. But you can get colds and flu in the summer - and cold sores too. Injury to the target area is a common trigger that causes cold sores. Sunlight is excellent for your skin, but sunburn is not. Sunburn commonly triggers cold sores. Burning your lip with hot pizza, or biting it, or kissing someone with an active cold sore can cause cold sores too. Any mental stress manifests itself physically, and is quite often responsible for causing cold sores. Some common "mental stress" triggers are upcoming events such as weddings, class reunions or presentations in front of people. Eliminating stress is the most often suggested solution for reducing, or preventing cold sores.

I'd say, kissing hookers.