I used to get what we called fever blisters (literal blisters/sores on the outside of your mouth) during the winter months when I was exposed to cold temperatures and they normally coincided with having a severe cold (accompanied by a fever).
"cold sores" (herpes) as I have come to understand them are smaller lesions on the inside of the mouth and I got them every now and they also coincided with having a cold but a less serious version (and possibly a different "cold" virus altogether.
I haven't had any since moving to a climate where catching a cold is less likely and exposure to large numbers of the population who probably have a cold is just as low.
There are products on the market which get rid of the "fever blisters", "Blistex" and "Carmax" are the two most popular.
Blistex always worked for me and Carmax always made them worse or gave me fever blisters if I ever used it in place of chapstick for a lip moisturizer so if you are using Carmax and have fever blisters often, that could be why...try Blistex, its great stuff.
