Barrista is referring to Shower Shock bar soap which, according to CosmeticsDesign , gives you the equivalent of 2 cups of coffee worth of caffeine every time you shower. This claim seemed a bit outrageous, so we did some digging. And guess what? Based on the published data, this is absolutely true! Imagine that – no more morning trips to Starbucks. No more messing with coffee grounds and filters! Now you can save a bundle on lattes while you lather up in the comfort of your own bathroom! Isn’t that amazing??
Oh, wait a minute. There’s just one catch. Bear with us here while we crunch the numbers.
First, how much caffeine is in a cup of coffee? It’s about 100 milligrams. So for two cups you’re looking at swallowing 200 mg. Can Shower Shock match that? Let’s see.
We have to establish that caffeine really does penetrate through skin into your blood. And indeed it does, according to PubMed . In fact, the diffusion rate for caffeine through human skin is 2.2 x 10-6 grams per centimeter squared of skin, per hour.
Ok, so now we know how much caffeine can penetrate 1 square centimeter of skin per hour. And since we know that the average human body has approximately 40,000 square centimeters of skin (look it up if you don’t believe us!), we can calculate how much caffeine can penetrate your entire body. According to my ciphering, that means your skin can absorb about 100 mg of caffeine in about an hour. So that means you’d have to stand in the shower for 2 HOURS before you’d get the equivalent of 2 cups of coffee in your system. That trip to Starbucks doesn’t seem like that bad of a deal now, does it?
Of course, we made some assumptions in this calculation, and if the fine folks who make Shower Shock would care to share their data, we’d gladly reconsider our findings. But without some kind of data to the contrary, this sounds like Marketing hype to the Beauty Brains . (And the same goes for other skin care products with caffeine, like Replenex.)