ELI5 Ultra Violet - should we bother with low SPF sunscreens?

How does UV light sanitize? If UV is dangerous for our skin, why bother with low SPF sunscreens? How does sunscreen work? What does the SPF number measure? What sunscreen products were recalled recently? ... we explain like I'm five Thank you to the r/explainlikeimfive community and in particular the following users whose questions and comments formed the basis of this discussion: runiat, jamaalfuckincharles, bobt21, isthisnamegood, charlesdparrott, dehacked, void_vix, uh-oh-cherio, y-void, thebearwillbefine, ribbitboing, opus666 and mleitch To the ELI5 community that has supported us so far, thanks for all your feedback and comments. Join us on Twitter: https://www.twitter.com/eli5ThePodcast/ or send us an e-mail: [email protected]