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這個很有趣
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Retinol vs Retin A
Many anti-wrinkle and skin rejuvenation products contain retinol, which is a form of vitamin A. Many people confuse retinol with Retin A, which is a brand of tretinoin also referred to as trans-retinoic acid or simply retinoic acid. Retinol and retinoic acid are related but distinctly different. Retinol and other forms of vitamin A, such as retinal and retinyl palmitate, do not have much direct effect on the skin. They first need to be converted by special enzymes into the active metabolite, retinoic acid. Only retinoic acid directly affects skin cells and helps reduce some signs of aging.
In theory, one should be able to apply retinol to the skin, wait till it gets converted to retinoic acid, and eventually get the known skin benefits of the latter. In reality, the conversion rate is low and varies greatly among individuals. Besides, when exposed to air either during storage or use, much retinol may get oxidized or degraded even before it can become availalbe for conversion to retinoic acid in the skin. As a result, significantly less people respond to retinol creams than to retinoic acid (tretinoin, Retin A), and the degree of response tends to be less too.
It is true that retinol products tend to have fewer side-effects than retinoic acid (tretinoin, Retin A). The reason is the same: lower biological activity of retinol due do slow conversion and, possibly, degradation. Notably, some companies have developed stabilized high-concentration retinol formulas that seem to be more effective than run-of-the-mill retinol products. However, high concentrations of retinol can be almost as irritating to the skin as retinoic acid |
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带你的孩子出去玩儿吧！(with Photo) (2009-9-22) pinkscooter 
楼主:chubbycat
发表于 2005-1-12 09:57
发表于 2005-3-8 10:34
