Very common with treatment. Not just the
sun but the heat as well. As far as
sun block is concerned, try and use a real block like with the Blue Lizard line of sun products uses. That way it works instantly. Fallene Cotz is another good one (check the internet if not local) as it contains only titanium and zinc, both blocks. But in addition to sun blocks you really should cover up with hats, shirts, etc, and ideally just stay in the shade.