...and prolonged unprotected sun exposure.
"In addition to the stratospheric ozone layer filtering the most harmful UVC, human skin contains a photoprotective pigment called melanin to protect from UVB, UVA, and blue visible light. This pigment is a redox UV-absorbing agent and functions as a shield to prevent direct UV action on the DNA of epidermal cells."
TL;DL Some people sunburn easier than others. It's not rocket surgery.
Best to know too that vitamin D is made ON the skin, acting as a natural sunblock. It’s then absorbed ~5-6 hours after exposure. Most people wash it off and don’t get any benefit. Ancestry determines how much and how quickly it’s produced too. Early day (before 10AM) sunlight supposedly penetrates deeper with more good UVA vs UVB later in the day. @AgoristView is right about O6/O3 levels in the epidermis and getting unstable industrial oils out of your diet and letting your body clear them from your skin and adipose tissue helps IME. I get a little pink, but don’t really peel any more - dose is the poison. Also think latitude plays a big role: https://jackkruse.com/the-sunshine-of-your-life/
Sorry, this is the latitude link: https://jackkruse.com/ubiquitination-8-the-mammalian-battery/ The whole ubiquitination series is good if you can get past his writing.
