Avobenzone, patented in 1973, is an oil-soluble ingredient of sunscreens that is said to absorb the full UV-ray spectrum. (Have you seen the term "full-spectrum sunscreen"?) However, toxicology tests show that when avobenzone is combined with chlorine (e.g., from swimming pools) and sunlight, it breaks down into other compounds -- alldehydes, phenols and chlorinated acetyl benzenes -- a couple of which are serious genotoxic carcinogens. Millions of people use sunscreens today. Most widely marketed sunscreens contain titanium dioxide (a heavy metal neurotoxin) and petrochemicals, neither of which are body-friendly.
Zinc-oxide sunscreens however (if it is not nano-zinc) are well-tolerated by human skin, and due to their matte texture, physically cover or protect skin from too much sun. Zinc oxide holds up well in water, too. See AvatarProducts.com for Bali Bloc zinc oxide sunscreen, and a particularly helpful product -- Zinc Oxide Body Wash -- which can be used in the shower to build zinc into areas of the body that are most exposed, resulting in a degree of "built-in" sun protection (especially good for men with thinning hair and bald heads).
What is "too much sun"? Melanin is a biopolymer that provides structure and thickness to the skin; dark people have more melanin than light-skinned people. Melanin also converts UV radiation into heat, and thus serves as a natural "sunscreen." However, even dark-skinned people can burn with extended sun exposure. Light-skinned people whose ancestry derives from colder regions with less sunlight are apt to burn much faster than dark-skinned people; hence suncreen can help, especially when applied to areas that get more exposure than others (nose, forehead, arms). Sunlight causes our body to produce Vitamin D, which triggers dozens of essential biochemical processes with the dawning of each day; therefore we do need sunlight for optimal health.