For years I would get cold sores and I could not figure out why.. I'm 70yrs now and about 5 years ago the answer came.. It was the sun that brought them on for me... I am fair skin and I have a large lot.. I do all the yard work , that includes making patios with pavers, digging up sewer pipes etc... The days I'm in the sun too long, the next day I will feel bumps next to my lips and I know whats coming Blisters... So now I do most of my yard work late in the day or very early in the am.. If I do get one, I use camphor.