In a recent cosmetic trade show, I saw it subtly being promoted as having a "stimulant" effect on skin itself. The truth is, the effects of caffeine are actually directly related to a metabolite of caffeine (paraxanthine), and not the caffeine itself. In essence, the caffeine has to reach the bloodstream and be metabolized by the liver to have any effect at all. And then, the effects of the metabolite (the product after the liver is through with it) are really just limited to muscular stimulation (mostly smooth muscle, such as that which lines your digestive tract) and nervous stimulation, both of which respond to elevated Calcium ion concentrations. And it can't possibly be localized to skin, because by the time it is metabolized, it is circulating in the bloodstream. There is no evidence that it does anything for your skin. But the marketing ploy is to suggest that it somehow has a "stimulating" effect on the skin. Some people will buy the propaganda though... Cheers, Alan:)