I'm curious about sun care products that don't contain SPF, like Institute Esthederm's products. They claim to work by building resistance to the sun vs. working like traditional SPF's. I haven't been able to use ingredients like Avobenzone/Oxybenzone because they make my skin sting, especially on my face. I've had better luck with Titanium dioxide/Zinc oxide but I still have some stinging with those as well. How would an SPF free product work to keep me from burning ( I am very pale) on days where I am exposed to the sun for a long period of time? And would they work better than traditional sunscreens? Institiute Esthederm also claims to build resistance for very sensitive skin types. Can anyone substantiate these claims?