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.

    我以前认为担心防晒霜中的遮阳剂就和担心海滨游泳袋差不多，给人带来的困扰就好比使用微波；在我看来，微波的节能能效毋庸置疑，相比之下，说明它有害的证据则不值一顾。对于防晒霜，我理性的判断是看重防晒霜"提供（deliver这个词来自化妆品行业词典）"的防护作用，比烦恼它本身的配方怎样重要的多。

    但后来，休息日里随意阅读时看到的一篇文章动摇了我以往的信心。意大利科学家在2008年的研究中发现防晒霜中的紫外线过滤剂导致了珊瑚礁褪色。（这是个不幸的生态巧合，防晒霜自身中的一种化合物正是用一种澳大利亚珊瑚礁中人工合成的。）研究人员称，每年大约会生产出10,000吨紫外线过滤剂，其中约有0.78亿旅游者购买了总量10%的紫外线过滤剂，在珊瑚区游玩时使用。浸泡在海水中20分钟就会有25%的防晒霜成分溶入水中，也就是说，每年海水中会溶解4,000~6,000吨紫外线遮阳剂，受影响的珊瑚礁达到了世界珊瑚礁总量的10%.令人惊讶的是，就算考虑到直接曝晒在太阳下对人体健康的危害，一些旅游景区现在还是明确写明"禁止使用防晒霜遮阳剂".

    就像是怕以前作用还不够似的，现在防晒霜遮阳剂包含的纳米粒子越来越多，比人类头发直径的千分之一还小。通常这会增加防晒霜遮阳剂的防晒指数（SPF）,使防晒霜更易干，可以融入皮肤，而不是在皮肤上糊一层白，要一天时间才能吸收。但是纳米粒子实在太微小，结果引发了大量争论。其中最主要的指责就是纳米技术应用泛滥，已经超出了控制。

    还不仅仅是这些。人们使用的护理产品中的帕拉胶和其他化学品也带来了种种困扰。2001年瑞士毒物学者Margaret Schlumpf进行了研究，她测试了6种紫外线屏蔽化学品，其中包括4-MBC.当4-MBC与橄榄油混合，涂在受创的皮肤表面时，会在青春期前，就让人体内的雌激素增长速度加倍，这种"模仿雌激素作用的性别扭曲化学品在防晒霜遮阳剂中颇为常见。"

    你可能会想，罢了，让那些爱好晒太阳的人投入所谓"天然"遮阳剂的怀抱吧。现在，有几种天然防晒成分已经买不到了，而只用人工合成化学物质显然是没法达到足够的防晒指数的。不过市面上还是有其他的强效遮阳剂可作为备选。这些遮阳剂可以生物分解，从其依赖氧化锌等物理隔离手段的角度来看，还颇为传统。消费道德杂志（ethical consumer）最新一期（www.ethicalconsumer.org）有一篇深入分析。的确，这些备选遮阳剂非常管用--尽管有些个只是折衷之选。在案例4里，绿色人群（Green People）使用纳米粒子、二氧化钛，他们认为这两种物质必不可少，而且很安全。

    或者你可以考虑用把阳伞或大檐帽，它们同样可以"提供"必不可少的防晒保护。