Sweating under the sun is good because that is how you get your vitamin D. However, you need not to shower for two days to make it work. You can shower but you can not use any type of soap to wash your skin yes, it's true.
You can visit Dr. Mercola's website if you don't believe me. And all this time I never gotten enough Vitamin D in my system. I always take a good shower after sunbathing when I was younger. Yes, I had the tan but no vitamin D from it. Interesting, I learn something new everyday.