I grew up thinking of myself as allergic to sun because if I got much sun I would have a headache and nausea that evening. Now I think what was going on was mostly dehydration. I am able to tolerate much more sun without getting a sunburn since I started taking vitamin D. I have also seen people say that eating a higher saturated fat diet increases sun tolerance. In recent years I have gotten a splotchy rash on my legs if I walk around a lot in the heat, but it happens even if I am wearing long pants so it isn't sun. I will be interested to see if that is different this years since going primal. You might start by exposing your arms and protecting your chest--take it one step at a time.