The sun's ultraviolet radiation is dangerous to our skin cells because it damages our DNA. That's why sun exposure can cause cancer, and why sunscreen is so important (even apart from its power to prevent sunburns). There are sunscreens that claim they can help your skin repair that damage — and, it turns out, they actually might (might!) work.
Some animals and bacteria produce DNA repair enzymes that we don't, Robbie Gonzales reports at Wired. Some of these are activated by sunlight, and preliminary studies show that they can actually be absorbed through human skin and protect DNA from radiation, as advertised.
But there are a couple of problems. One is that we only have a few lab studies to go on, not a solid body of evidence. Another is that these enzymes haven't gone through the FDA approval process, and aren't widely available.
But the biggest issue is simply that they're expensive. Estée Lauder makes them, Gonzales found, and sells them to other cosmetics companies who want to make DNA-repairing sunscreens as a pricey niche product. Three to 120mL will run you anywhere between $60-$100 depending on the brand. That's enough for maybe a couple of days of responsible sunscreen use.
So don't expect these formulas to replace your regular sunscreen any time soon.