SPF 50. BecauseSPF 30 allows about 3 percent of UVB rays to hit your skin. An SPF of 50 allows about 2 percent of those rays through. That may seem like a small difference until you realize that the SPF 30 is allowing 50 percent more UV radiation onto your skin.

Yes,absolutely. There are two different types of sunscreen: traditional “chemical” sunscreens and “chem-free”. The words “chemical” and “chem-free” refer to the active ingredients, but they are a misnomer. Chemical sunscreens contain carbon-based active ingredients, such as avobenzone, to protect the skin. These ingredients work by aligning on your skin in a lattice-form, and absorbing and thereby neutralizing the harmful UV rays. Once applied to your skin, it takes some time to form their protective lattice barrier, so they need to be applied a half-hour before sun exposure. Chem-free sunscreens should be called “carbon free” because instead of using carbon based actives to protect from UV, they use one or two mineral based active ingredients (which of course are “chemicals”, just not carbon based chemicals): titanium dioxide and zinc oxide. These ingredients act to literally block and reflect the damaging rays of the sun from your skin. They work immediately after application.