I used to think that worrying about sunscreens was the beach-bag equivalent of angsting about using a microwave: the latter's energy-saving credentials and a lack of evidence of harm overrides doubt for me. And with sunscreen I reasoned that the protection it "delivers" （to borrow from the cosmetic industry's lexicon） outweighs any niggling doubts about its ingredients.

    But then a little light holiday reading began to erode my confidence. Turns out that a 2008 study by Italian scientists found that UV filters in sunscreens causes coral bleaching. （This is an unfortunate ecological coincidence, as one of the original compounds for sunscreen was synthesised from an Australian coral reef.） According to researchers, 10,000 tonnes of UV filters are produced every year, about 10% of which are used by the 78 million tourists visiting sensitive coral areas. As a 20-minute slathered-up dip in the sea is enough to wash off 25% of the ingredients into the water, 4,000 to 6,000 tonnes of UV sunscreen are released annually into the sea, affecting 10% of the world's coral reefs. Amazingly, given the risk of sun exposure to our health, some resorts now specify "no sunscreen".

    As if that were not enough of an impact, sunscreens increasingly contain nanoparticles, smaller than one one-thousandth the diameter of a human hair. Often this simply enables a sunscreen with a sun protection factor （SPF） to dry clear and disappear into the skin rather than forming a white paste that takes all day to rub in. But for something so tiny, these nanoparticles cause massive debate, the main charge being that their application has outrun regulation.

    There's more. Alongside unease about parabens and other chemicals common in personal care products, 2001 research by Swiss toxicologist Margaret Schlumpf tested six UV-screening chemicals, including one known as 4-MBC. When the latter was mixed with olive oil and applied to rat skin, it doubled the rate of uterine growth well before puberty, which led to claims that "gender-bending chemicals that mimic the effect of oestrogen are common in sunscreens".

    Enough, you might think, to drive many sunseekers into the arms of "natural" sunscreens. Except that a couple of the originals have disappeared from sale, apparently unable to provide sufficient SPF without help from man-made chemicals. But there are still some strong alternative sunscreens out there that are biodegradable and possibly old-fashioned, in the sense that they rely on a physical barrier, like zinc oxide. The current issue of Ethical Consumer （www.ethicalconsumer.org） contains an in-depth review. And yes, they do work - although some represent a compromise. Green People, for example （4）, uses a nanoparticle, titanium dioxide, which it considers both necessary and safe.

    Or you might consider a parasol, or large-brimmed hat, both of which will "deliver" vital protection.

    我以前認為擔心防曬霜中的遮陽劑就和擔心海濱游泳袋差不多，給人帶來的困擾就好比使用微波；在我看來，微波的節能能效毋庸置疑，相比之下，說明它有害的證據則不值一顧。對于防曬霜，我理性的判斷是看重防曬霜"提供（deliver這個詞來自化妝品行業詞典）"的防護作用，比煩惱它本身的配方怎樣重要的多。

    但后來，休息日里隨意閱讀時看到的一篇文章動搖了我以往的信心。意大利科學家在2008年的研究中發現防曬霜中的紫外線過濾劑導致了珊瑚礁褪色。（這是個不幸的生態巧合，防曬霜自身中的一種化合物正是用一種澳大利亞珊瑚礁中人工合成的。）研究人員稱，每年大約會生產出10,000噸紫外線過濾劑，其中約有0.78億旅游者購買了總量10%的紫外線過濾劑，在珊瑚區游玩時使用。浸泡在海水中20分鐘就會有25%的防曬霜成分溶入水中，也就是說，每年海水中會溶解4,000~6,000噸紫外線遮陽劑，受影響的珊瑚礁達到了世界珊瑚礁總量的10%.令人驚訝的是，就算考慮到直接曝曬在太陽下對人體健康的危害，一些旅游景區現在還是明確寫明"禁止使用防曬霜遮陽劑".

    就像是怕以前作用還不夠似的，現在防曬霜遮陽劑包含的納米粒子越來越多，比人類頭發直徑的千分之一還小。通常這會增加防曬霜遮陽劑的防曬指數（SPF）,使防曬霜更易干，可以融入皮膚，而不是在皮膚上糊一層白，要一天時間才能吸收。但是納米粒子實在太微小，結果引發了大量爭論。其中最主要的指責就是納米技術應用泛濫，已經超出了控制。

    還不僅僅是這些。人們使用的護理產品中的帕拉膠和其他化學品也帶來了種種困擾。2001年瑞士毒物學者Margaret Schlumpf進行了研究，她測試了6種紫外線屏蔽化學品，其中包括4-MBC.當4-MBC與橄欖油混合，涂在受創的皮膚表面時，會在青春期前，就讓人體內的雌激素增長速度加倍，這種"模仿雌激素作用的性別扭曲化學品在防曬霜遮陽劑中頗為常見。"

    你可能會想，罷了，讓那些愛好曬太陽的人投入所謂"天然"遮陽劑的懷抱吧。現在，有幾種天然防曬成分已經買不到了，而只用人工合成化學物質顯然是沒法達到足夠的防曬指數的。不過市面上還是有其他的強效遮陽劑可作為備選。這些遮陽劑可以生物分解，從其依賴氧化鋅等物理隔離手段的角度來看，還頗為傳統。消費道德雜志（ethical consumer）最新一期（www.ethicalconsumer.org）有一篇深入分析。的確，這些備選遮陽劑非常管用--盡管有些個只是折衷之選。在案例4里，綠色人群（Green People）使用納米粒子、二氧化鈦，他們認為這兩種物質必不可少，而且很安全。

    或者你可以考慮用把陽傘或大檐帽，它們同樣可以"提供"必不可少的防曬保護。