An unpleasant new study suggests sunblock just isn't enough to prevent skin cancer. This likely comes as a shock to you, as most folks polled aren't that worried about sun damage.
Sunscreen itself works because it contains chemical groups known as carbonyls. These bonds have the ability to absorb damaging ultraviolet rays and release that energy as lower wavelength emissions in the form of heat or other radiation. Contrast that to heavy clothing which also absorbs the radiation but also reflects a portion, thus providing a more robust shielding from the rays.
Ninety percent of all skin cancers are directly a result of sun damage.
Paul Verhoeven, in his seminal work, Robocop, laced the film with a couple of very notable faux commercials, satirizing a dehumanizing capitalistic system with his dystopic vision. Unfortunately for us, it might be more factual than we hoped.