text: what causes a cold sore?   typically, cold sores are caused by contact with an infected source. most commonly, cold sores near and around the mouth are caused by oral sex or oral contact with another person infected with cold sores. next time, i suggest taking a closer look at the area you are about to put your mouth on. "if there's a sore, don't lick no more" is a good rule of thumb. if you have now experienced a recent outbreak of cold sores, pat yourself on the back- you now have herpes for the rest of your life, just like 1/4 of the population!