GENETIC analyses of human skin are revealing more about what makes us look old. As well as throwing up ways to smooth away wrinkles, the studies may provide a quantifiable way to test claims made for skin products.

    In the past, cosmetics companies relied on subjective assessments of skin appearance, and changes in its thickness, colour and protein composition, to evaluate the effectiveness of their products and work out the quantities of ingredients needed to get the best results. "It was totally hit and miss," says Rosemary Osborne of Procter and Gamble in Cincinnati, Ohio.

    Now skin researchers, including those at P&G, are starting to use DNA microarrays, common in the drugs industry, to measure the expression of thousands of genes in skin of different ages. "It's a way of finding mechanisms that were not known before," says Fernand Labrie, who studies skin genomics at Laval University in Quebec City, Canada.

    P&G recently compared gene expression in skin samples from the buttocks and forearms of 10 young and 10 older women. In older skin, they found a decrease in the expression of genes involved in cholesterol and fatty acid synthesis. More surprisingly, the opposite was true for genes associated with inflammation and other components of the immune system, suggesting that the immune system may play a role in ageing.

    Treating the older skin with niacinamide, which helps skin retain moisture, damped down expression of genes related to inflammation. "We believe that improving the barrier results in a 'resignalling' of key molecular components of the skin," says Jay Tiesman of P&G. Targeting this inflammation might one day help to keep wrinkles at bay. The findings will appear in the Journal of Drugs in Dermatology in July.

    Identifying a "genetic signature" of younger skin should also provide a benchmark for testing existing skin products. For example, P&G is measuring the effects on gene expression of a skin cream ingredient called pal-KT. Previous approaches suggested it increased production of structural skin proteins like collagen and laminin. Gene analysis indicates it also affects the expression of genes involved in wound healing.

    P&G isn't alone, cosmetics firm L'Oréal claims to have identified differences in the way genes in old and young skin respond to physical damage: changes in gene expression began just 6 hours after damage in young skin but took around 30 hours to kick in with older skin. What's more, around 25 genes differ in their response to skin damage in young and old skin, says L'Oréal.

    Rigorous studies in people are needed to confirm that changing gene expression in older skin to match younger skin improves skin quality. "You could find that a molecule is up or down-regulated, but whether that relates to a consumer noticing a difference is a big jump," says Diona Damian at the University of Sydney, Australia.

    If new tools become available for assessing skin products, this could force cosmetics companies to back up claims about their products with hard evidence.

    "If you really want to bring cosmetics into the field of rigorous scientific evidence, genomics may be the best and most quantitative way of doing it," says Labrie.

    究竟是什么讓我們看起來衰老，通過對于人類肌膚的基因分析，更多奧秘正在浮出水面。這些研究提出了很多平復皺紋的方法，也提供了幾種可以用來測試化妝品公司所聲稱的護膚品功效的辦法。

    過去，化妝品公司都是依靠對肌膚整體外觀的主觀評定，以及肌膚厚度、膚色和蛋白質組成的變化情況，來衡量其產品的效力，以確定要達到最佳效果所需的各種配方。"完全就是一點一點試出來的。"來自俄亥俄州辛辛那提寶潔公司的羅斯瑪麗。奧斯本說。

    目前，很多皮膚研究員，包括寶潔公司的皮膚研究員，已經開始使用制藥業中常用的DNA微序列來分析不同年齡肌膚中上千基因的表達式。"用這種辦法可以發現一些以往未可知的機理。"在加拿大魁北克市拉瓦爾大學研究肌膚基因組學的費爾南多。萊柏瑞說。

    寶潔最近在一項研究中取10位年輕女性和10位年長女性的臀部和前臂肌膚樣本，比對其基因表達。研究發現，年長者的肌膚中膽固醇和脂肪酸合成物的基因表達有所衰減。然而更令人驚訝的是，與免疫系統中炎癥和其他成分相關的基因卻正好相反-表達有所增長，這說明免疫系統在衰老的過程中起了很重要的作用。

    用有助于保濕的煙酰胺來處理衰老肌膚，可以使與炎癥相關基因的表達式有所衰減。"我們相信通過阻礙其增長，可以使肌膚的關鍵分子組成'重新發出信號'."寶潔公司的杰伊。緹斯曼說。針對炎癥細胞的各種措施，很有可能能夠有效地牽制皺紋的生長。這些發現結果將會刊登在7月的Journal of Drugs in Dermatology .

    對于年輕肌膚"基因簽章"的識別，同樣也會為現有的各種護膚品提供測試基準。例如，寶潔正在測量潤膚霜中一種叫做"pal-KT"的成分對于基因表達所起的效用。之前的研究結果顯示它可以增加膠原蛋白、層粘連蛋白等肌膚結構蛋白的生成。基因分析表明它對與傷口愈合相關基因的表達也有一定作用。

    寶潔并非唯一在做此類研究的公司，歐萊雅聲稱已發現年老和年輕肌膚中，基因對于物理性損壞的反應有所不同：年輕肌膚損傷6小時后，基因表達即有變化，而年老肌膚則需要30小時左右。更有甚者，二者相比，約25種基因的反應有差異，歐萊雅說。

    改變年老肌膚的基因表達式，使其與年輕肌膚相同，可以有助于改善肌膚質量-要證實這一點還需要做很多縝密的研究。"你可能會發現某種分子被人為控制增長或衰減，但它引起的差異是否能被消費者注意到，這是一個飛躍。"澳洲悉尼大學的戴奧娜。達米安說。

    如果這種評定護膚品的新辦法研制成功，化妝品公司將會被強制要求提供確鑿證據來證明其聲稱的產品功效。

    "如果你確實想找到能證明化妝品功效的嚴謹的科學依據，那么基因組學是最佳的量化分析的辦法。"萊柏瑞說。