Slip slop slap. It's an all too common slogan preceding some fun in the sun but a recent study into sun exposure and it's effects on the skin will give you some food for thought and may very well change your mind.
Researchers have published results in a prominent Cancer Journal that dispute the commonly held ideas about avoiding the sun and so as far as stating that sunlight prevents cancer. There are many points made including that absence of D vitamin (derived from sun exposure) actually sets us up for other cancers. There are sensible limits to be observed and diet related issues to consider.
Dr Mercola additionally explains that it is excess of Omega 6 fats (common with high grain consumption) in addition with excess exposure ie sunburn that should be considered dangerous.
More discussion of these points can be found here.
You may be also interested in this article on Nano technology in Sunscreens. It can be found here.