As a teen my acne would clear up immediately for weeks after getting a bit sunburnt on my face. Very much regret not sunscreening sufficiently now because of the increased skin cancer risk I took on. But I was told this happened because the sunlight killed off the bacteria on my face. I figured out recently that homemade hypochlorous acid does the same thing and is completely safe, and indeed, it is extremely effective at controlling my adult acne. .
It's the most effective single chemical I've used for acne and I've tried a lot of stuff!
I bought a water electrolyzer from Amazon. (You can also apparently make your own but I haven't tried.) Fill it with distilled water, add vinegar to adjust pH (important, otherwise you can accidentally make bleach), weigh out a couple grams of non-iodized salt, then run for like 15-30 minutes and bam. If you're using it on your face you should definitely get chlorine test strips to make sure it's not too high ppm.
It gradually loses efficacy and reverts to water after a week or two, so I make more regularly. I put it in a mister bottle and spray it on my face multiple times a day. It's refreshing and doesn't seem to cause any irritation, even when I use it a lot.
For me it's cost, convenience (not having to remember to buy something regularly), less waste - but I also use hypochlorous for other household disinfecting so making large quantities is useful to me. If you're just doing skincare with it, I can see it making sense to buy it premade, especially at first when you don't know how much you'll like it. Though I will note that, while the information can be intimidating at first, once you make it a couple times it's extremely simple going forward. Now that I know the ratios of vinegar and salt I need for my own machine, I just dump things in and run it and it's good every time without having to make any adjustments.
I’ve never explicitly tanned before but whenever I get a buzz cut and my scalp gets some sun it goes away. Also heard it could be triggered by insulin resistance (which I also have)