There are two main types of sunscreens: physical (mineral or inorganic) and chemical (organic). Physical screens (zinc oxide and titanium dioxide) work by deflecting UV rays, while chemical screens work by absorbing them (instead of your skin doing so). The trouble with physical screens, as Aasi says, is mostly that "people don't like the look." Sunscreen makers have solved that problem by using micronized versions of the minerals — "Very few are really nanoparticles," Rigel says — and the EWG says there's no evidence that the minerals, even in miniature form, can penetrate the skin and do any damage. Among chemical sunscreens, the group recommends using those that contain 3% avobenzone (for UVA protection) and avoiding "the notorious hormone disrupter oxybenzone."