We all know how vital it is to scrupulously use a daily sunblock. In that broad-spectrum sunblock also look for the very important protective ingredients of zinc oxide and titanium dioxide. And, by the way, The FDA states that SPF of 15 is adequate.
Skin cancers can form even with and after use of sunscreens due to previous UV exposure.
But, sunscreens more than anything else will reduce the risk of additional UV damage. There is never a bad time to start using a sunscreen or sunblock. Very few make-up foundations contain higher numbers. If you find one that does have an SPF 15, then grab it, but if you can't find one, then be sure to wear an SPF 15 sunscreen under your foundation. Even though sunblocks and sunscreens are essential, there are other products that can even increase the effectiveness of the sunblock.