As one who is also uber fair with a huge family history of skin cancer, and having had several removed from me already and the scars to prove it, plus living my whole life at altitude and in the desert...

...I do not trust that most conventional sunscreens are good for us. They may keep us from being burned, but they are full of crap I simply do not trust. After slathering on spf 30's to 50's of the conventional variety for years to no good effect (in terms of preventing skin cancer)...

I have switched to mostly chemical free sunscreens, none over the level of 20 spf, and I also do the Vitamin D supplement thing. Not only do I feel better, I haven't had the yearly "bloom" of basal cell carcinomas I was starting to bitterly agree to.

I strongly suspect the efficacy of sunscreens in their ability to prevent cancer. They may prevent burn, but I don't believe most are good for us due to their heavy chemical make up, and create more problems than they prevent.