With the possible exception of smoking UV exposure is known to be the single greatest contributor to premature/accelerated skin aging. If that is a concern for you the take away should be to wear sunscreen everyday and reapply frequently (the general recommendation is every two or three hours but we'll touch on this further).
The FDA hasn't approved any new sunscreen active ingredients in over a decade and as a result the USA has become a bit of backwater in sunscreen technology relative to Europe and Australia. Many of the older chemicals which have been approved have some issues with photo-degradation (part of the reapply frequently recommendation), hormonal activity, skin absorption, and the generation of free radicals with time and UV exposure. Newer active chemicals don't appear to exhibit these issues or only have them to a far lesser degree. They may have other problems but, so far, they appear safe after more than a decade of use in Europe.
Mineral sunscreens, zinc oxide and titanium dioxide, are effective in high enough concentrations although less so that some of the newer chemicals. They don't photo-degrade and they aren't hormonally active but they can form free radicals. Zinc oxide alone is effective across a significantly wider range of UV wavelengths than titanium dioxide alone. The downside of mineral sunscreens is that they leave a white cast and the stronger the sun protection the whiter the film. It is impossible to totally eliminate this at high SPFs but the two methods used to minimize it are to add a tint (some of which can stain clothes) and/or to reduce the particle size (nano although the term is used loosely in sunscreens). There are some remaining question marks about nano zinc oxide and nano titanium dioxide and the particles are usually coated. At least theoretically you could go longer than two hours without reapplying mineral suncreens (or some of the newer chemistry below), perhaps as much as four hours, but there are still concerns about them rubbing off or washing off. Some people find mineral sunscreens less irritating than chemical sunscreens but that, at least arguably, may have more to do with the carriers than the active ingredients.
The newer sunscreen actives: Tinosorb S and Tinosorb M, Uvinul A+ and Uvinul T150, Mexoryl XL and Mexoryl SX, Uvasorb HEB, and Bisdisulizole Disodium look like major improvements but, so far, there is no US availability. Canada has recently adopted European sunscreen standards and some of these are starting to appear in suncreens available in Canada.
Avobenzone aka Parasol 1789 is widely used in the USA and still shows up in some foreign suncreen formulas. It can stain clothes if the laundry water contains any significant level of iron. It also significantly photo-degrades but it is far from the worst of the old school actives. Padimate O aka Octyldimethyl PABA or Ethylhexyl dimethyl Paba, Octyl methoxycinnamate aka Ethylhexyl Methoxycinnamate or EHMC or Octinoxate, Homosalate aka Homomethyl salicylate or HMS, and Octocrylene aka OCR are all widely used sunscreen chemicals I'm personally trying to avoid but as always YMMV.
The Derma suncreens from Denmark, Uncover suncreens fro the Netherlands, Ultrasun from Switzerland (they also have a UK office) and Biodermal (Netherlands but sold under the ACO name in Sweden) are all using mostly or exclusively the newer chemistry. Of these, Ultrasun seems to be the easiest to obtain in the USA. There are probably other equally good marques but these are the ones I'm aware of. La Roche Posay has some suncreens available in Canada that use partially, but not exclusively, the newer chemistry. The suncreens sold through La Roche Posay USA do not use the newer chemistry.
The FDA hasn't approved any new sunscreen active ingredients in over a decade and as a result the USA has become a bit of backwater in sunscreen technology relative to Europe and Australia. Many of the older chemicals which have been approved have some issues with photo-degradation (part of the reapply frequently recommendation), hormonal activity, skin absorption, and the generation of free radicals with time and UV exposure. Newer active chemicals don't appear to exhibit these issues or only have them to a far lesser degree. They may have other problems but, so far, they appear safe after more than a decade of use in Europe.
Mineral sunscreens, zinc oxide and titanium dioxide, are effective in high enough concentrations although less so that some of the newer chemicals. They don't photo-degrade and they aren't hormonally active but they can form free radicals. Zinc oxide alone is effective across a significantly wider range of UV wavelengths than titanium dioxide alone. The downside of mineral sunscreens is that they leave a white cast and the stronger the sun protection the whiter the film. It is impossible to totally eliminate this at high SPFs but the two methods used to minimize it are to add a tint (some of which can stain clothes) and/or to reduce the particle size (nano although the term is used loosely in sunscreens). There are some remaining question marks about nano zinc oxide and nano titanium dioxide and the particles are usually coated. At least theoretically you could go longer than two hours without reapplying mineral suncreens (or some of the newer chemistry below), perhaps as much as four hours, but there are still concerns about them rubbing off or washing off. Some people find mineral sunscreens less irritating than chemical sunscreens but that, at least arguably, may have more to do with the carriers than the active ingredients.
The newer sunscreen actives: Tinosorb S and Tinosorb M, Uvinul A+ and Uvinul T150, Mexoryl XL and Mexoryl SX, Uvasorb HEB, and Bisdisulizole Disodium look like major improvements but, so far, there is no US availability. Canada has recently adopted European sunscreen standards and some of these are starting to appear in suncreens available in Canada.
Avobenzone aka Parasol 1789 is widely used in the USA and still shows up in some foreign suncreen formulas. It can stain clothes if the laundry water contains any significant level of iron. It also significantly photo-degrades but it is far from the worst of the old school actives. Padimate O aka Octyldimethyl PABA or Ethylhexyl dimethyl Paba, Octyl methoxycinnamate aka Ethylhexyl Methoxycinnamate or EHMC or Octinoxate, Homosalate aka Homomethyl salicylate or HMS, and Octocrylene aka OCR are all widely used sunscreen chemicals I'm personally trying to avoid but as always YMMV.
The Derma suncreens from Denmark, Uncover suncreens fro the Netherlands, Ultrasun from Switzerland (they also have a UK office) and Biodermal (Netherlands but sold under the ACO name in Sweden) are all using mostly or exclusively the newer chemistry. Of these, Ultrasun seems to be the easiest to obtain in the USA. There are probably other equally good marques but these are the ones I'm aware of. La Roche Posay has some suncreens available in Canada that use partially, but not exclusively, the newer chemistry. The suncreens sold through La Roche Posay USA do not use the newer chemistry.
