上回有篇post也是有关日晒，很抱歉我分享的内容有一些错误， 已经编辑予以更正。 底下我分享一些整理基础知识、名词介绍、 以及个人认知下的简单建议. 有所不足的请给我建议或更正、补充。 1. 认识紫外线 http://en.wikipedia.org/wiki/Ultraviolet 这太基础不赘述。有必要再予以补充说明。 2. 紫外光致黑机制 2.1 UVA 和 UVB的作用 引用 http://teenhealth.about.com/od/bodyimage/a/howtanninghappens.htm How UV Rays Cause a Tan 紫外线如何导致晒黑 UV rays cause tanning by the way they affect the melanin in our skin. Melanin is a pigment in our skin and is what gives our skin its color. * UVA causes a tan by oxidating the melanin. Essentially, the melanin undergoes a chemical reaction after being exposed to UVA, causing it to become darker. When the melanin looks darker, the skin itself looks tanned and dark. 节译: UVA会导致麦拉宁黑色素的氧化，而加深它的颜色. * UVB causes a tan in a different method. UVB causes an increase in production of melanin in the skin and other changes to the cells that the melanin is stored in. These UVB effects cause the skin to become darker or tanned. 节译: UVB不同, UVB会促进黑素细胞 产生麦拉宁黑色素. 提高麦拉宁黑色素储存量. UVB也会造成麦拉宁黑色素颜色加深. 2.2 DNA的伤害 引用 http://en.wikipedia.org/wiki/Melanogenesis Since the action spectrum of sunburn and melanogenesis are virtually identical, it is assumed that they are induced by the same mechanism.[8] The agreement of the action spectrum with the absorption spectrum of DNA points towards the formation of cyclobutane pyrimidine dimers (direct DNA damage). The acronym for cyclobutane pyrimidine dimers is CPDs. 节译: 黑素生成(melanogenesis)与晒伤 其作用的波段是相同的， 故一般假设有相同的机制。 晒黑作用区段与DNA吸收光谱的一致，指出它是来自DNA的直接伤害 (CPD) ref: Nita Agar; Antony R. Young (2005). "Review: Melanogenesis: a photoprotective response to DNA damage?". Mutation Research/Fundamental and Molecular Mechanisms of Mutagenesis 571 (1-2): 121–132. 解释: DNA伤害之後 细胞藉由甲硫氨酸和叶酸等物质 有一定的修补机制。 不过这边就要注意了： 假如一个促进晒黑的方式，是藉由增加DNA伤害而达成， 那可以说是一个不好的方法。 因为越多DNA伤害，意谓着细胞病变机率越高。 目前理解, DNA伤害是皮肤晒黑一个必经的机制。 3. 有人根据UVA & UVB 的特性 拟定了日晒策略 《UVB to build a tan. UVA to maintain it》 http://www.tan-biz.co.uk/fileadmin/all/tanbiz/UK/downloads/2007/01_2007/ TBUK0701_55_web.pdf UVB to build a tan You only need a little UVB to stimulate the melanin producing cells (melanocytes) into producing extra melanin ‘parcels’. It must be enough to trigger melanin production but no more; any more than this will simply result in cell damage (erythema, or sunburn). Initially, after winter, pale skinned persons don’t need any UVA in their first few sessions because the priority here is to start up the little melanin factories (melanocytes) in the skin and this takes a few days. Any UVA they do receive is wasted – it produces very little effect (there is not enough melanin around after winter in skin type 2 persons, particularly) and as a result is absorbed by the wrong molecules (not melanin, which is largely absent until after the first few sessions, but more vulnerable and unprotected parts of the skin). This causes free radical damage and may affect cell DNA temporarily, or even permanently. There appears to be no reason why we could not use a theoretical‘Type 3’ lamp which produced only UVB for the first couple of sessions. This would concentrate on making melanin that later sessions could then brown using mainly or purely UVA. UVB is needed to build a tan by creating more melanin in the first place. 节译: 靠UVB来建立晒黑的基础 你只需要一点 UVB 的剂量 来刺激黑色素细胞进入多量的麦拉宁生产状态. UVB必需要够多来引发麦拉宁生产，但是不需要更多。更多的剂量只会造成细胞伤害。 (红班或晒伤) 在初始阶段，或刚过冬天，苍白皮肤的人前几次晒不需要UVA，因为此时优先的事情是 启动皮肤上的小小麦拉宁工厂让它开始生产。这将要花费数天。此时UVA的照射是浪费 的，它只产生很少的作用 (因为皮肤中没有足够的麦拉宁)。结果UVA将由不是预期中的 分子吸收，因而引起自由基或是暂时甚至永久影响细胞的DNA. (後段广告自家商品就不翻译了) UVA to maintain a tan Once melanin ‘parcels’ start to be produced by the melanocytes after being triggered by UVB(2), they migrate into the upper layers of skin where they spread out to cover the DNA-containing cell nuclei and so protect them (like umbrellas, or sun shades!). At this stage the melanin is white (not exactly, but very pale anyway) not brown. In order to turn brown it needs to be bombarded with UVA, which is where our high intensity UVA tanning lamps come in. The higher the intensity of UVA the darker the tan in shorter session times. To get this dark with lower intensities of UVA you need a longer session time – and this may be ideally suitable for the beauty sector. Longer session times are also more efficient at browning melanin and it is possible to get a better result with less cell damage from a longer, weaker session. Once the melanin production is kick-started by UVB, you only need a little UVB to trigger continued production so it makes sense to concentrate more on UVA once the tan starts to appear. Alternating two or three UVA sessions to one UVB session could be a way of deepening a tan using type 3 intensity tanning lamps. You might, say, devote one sunbed out of three, four, or five, to exclusively using UVB lamps and the rest to UVA. UVA is needed to ‘brown’ or maintain a tan. A good tan needs both UVB and UVA, but in differing amounts at different times and not necessarily together. 节译: 靠UVA来维持深肤色 一旦UVB照射引发黑色素细胞开始生产麦拉宁，这些麦拉宁被传送到皮肤的上层，并且 散布开并且盖住含有DNA细胞核的细胞 (像一把伞或是遮阳)。在这个阶段麦拉宁 仍然是白色的 (严格讲不是白色, 但是是非常浅色的) 而非褐色。要把它转为褐色， 它需要UVA的 '轰炸'. UVA强度越高所需的时间越短，如果想靠低强度的UVA光源 你会需要晒较长的时间。 较长的晒肤时间，对於加深麦拉宁的颜色也较有效率；这种低强度-长时间的晒肤 结果较好，细胞伤害较小。 一旦UVB照射启动麦拉宁制造，你只需要少量的UVB来维持它持续制造。 所以一旦肤色加深了 专注在UVA是合理的。 However, if the best guide to safety is the composition of natural sunlight, then we had best stick to mainly UVA with a little UVB. It’s not an exact match, but the closest in terms of practical application in a commercial setting. Clearly, there is stillsome way to go with this infant subject but it may hold the future of tanning. 4. 助晒 tanning activator http://en.wikipedia.org/wiki/Tanning_activator 这个wiki解说了目前已知助晒的机制. Mechanism of tanning activators The increased production of melanin is the reaction of the skin to UVB-induced direct DNA damage.[6] Several substances are known to increase the amount of direct DNA damage (thymine dimers). In order to produce this action they have to penetrate into the skin, and this is in contrast to the assumptions which are made by those who endorse sunscreen use (see sunscreen controversy). 节译: 麦拉宁黑色素的产生增加，是来自皮肤对於UVB引发的DNA伤害。 有数种化物是我们已经知道可以增进DNA伤害.(thymine dimers 是一种DNA伤害.) The tanning activator coumarin is known to induce thymine dimers (cyclobutane pyrimidine dimers). 节译: 助晒成份 香豆素coumarin 已知是会造成CPD伤害的。 解说: 香豆素的这种作用，是一种光敏性。 --

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