Allow me to be your poster child for what not to do when outside.
I'm the first to advise all to wear sun screen, not to sunbathe in direct sunlight with no protectant and to generally avoid prolonged exposure to the sn.
So off I trot, out to our deck having slathered my kids in a very high factor sunscreen about 15 minutes before hand. The huge umbrella is up and I sit beneath it, watching my children splash in their little pool. A couple of hours and a nice lunch later, I put everyone down for naps and continue my day.
And later that day I look in horror to see my entire upper half burned, from sitting in the shade for two hours. I always know that sun can still 'get' you in the shade but since I was entirely covered for the two hours, and feeling cool from the shadow cast by the umbrella, I neglected to put my sunscreen on and paid a hefty price. The burn wasn't too bad but certainly covered my shoulders, arms and chest. I lamented I was on my way to getting 'old lady chest' - that kind of copped-colored wizened up chest that I've seen older Floridans sporting from years of sun exposure. Not to mind the kind of damage it can do.
The burn has gone now and I am nicely tanned, although it was purely unintentional. A nice tan isn't worth it! And this reminds me to always protect myself, no matter how much I remain in the shade. The same goes for cloudy days. Clouds don't offer much protection either. The sun's rays have a very long arm, indeed. And with skin cancer being the most common cancer of all (one million non-melanoma cases in the United States every year!) mistakes like I made need to be avoided at all cost.
For more information on how to protect yourself from too much sun click here
or here