me too... when i saw a photo of myself at 6 yrs old, tan, and with a great big cold sore on my lower lip... i didn't put the sun and cold sore correlation together... but every time i get a sunburn, i get a cold sore.
now i have to always cover my lips in zinc oxide, when i go in the sun..

I've only ever gotten a fever blister when I get sunburn. I was once burned by a UV light at work, and it was the most massively painful thing I've ever suffered...

The last time (literally in YEARS) that I got a fever blister was in January... when my truck died in a remote location and I had to wait FOUR HOURS on a tow truck. I'm grateful it was a warm January day and not freezing.

When I get a fever blister, I take a lot of Zinc and Vit C. And one thing else... IF you can catch it EARLY... (first tingle) and can ICE your lip down for maybe fifteen minutes... it WON'T form a blister. The chilling stops the virus from replicating. Won't help if you wake up with one, but if you can catch it early...

sun exposure = fever blister
good thing i'm not one to go in the sun for very long.