Sour cream corny moisturizes the skin. Like baby cream, for example. And better - panthenol, specially created by smart people for these purposes. Such things.
It is best to apply sunscreen before the burn for sunburn. Oh yes, then there will be no burn at all. I am very very worried about people who burn themselves every summer and then seek salvation in fermented milk products. I urge you to urgently buy a cream with an SPF (protection factor) of 30 and above (these are such huge numbers that are written on the label). The sun not only ages the skin, but also causes, for example, cancer. Don't mess with the sun, please.
If you are already burned, then, firstly, draw conclusions, and secondly, abundantly use any moisturizing and nourishing products on the site. Cold sour cream will simply cool, and the cream will begin to heal and regenerate the skin. Aloe gel helps very well, such a transparent pleasant thing, I advise you to have it in your arsenal.
Good luck and please avoid sunburn!