Today’s Friday Weird Science was inspired by @TruffledSquirrel, Who sent me the following tweet.
@scicurious you love science & coffee; any idea how much caffeine you can actually absorb through your skin? thisiswhyimbroke.com/caffeinated-so…
— Joanna Martin (@trufflesquirrel) February 21, 2013
The link listed is to this product:
This is Shower Shock, caffeinated soap. And in fact, I have personal experience with it! Someone gave it to me as a gift, figuring that anything caffeine-themed would go over well. They were correct, but unfortunately, I have extremely sensitive skin and couldn’t use the soap. 🙁
But I, like @trufflesquirrel, have always wondered if it worked. I have to admit I basically assumed that it was a gimmick. I mean, caffeine absorption through the skin? The claims are as follows:
Shower Shock is an all vegetable based glycerine soap which does *not* contain any harsh ingredients like ethanol, diethanolamine, polyethylene glycol or cocyl isethionate. So it’s a gently invigorating soap 😉 Scented with peppermint oil and infused with caffeine anhydrous, each bar of Shower shock contains approximately 12 servings/showers per 4 ounce bar with 200 milligrams of caffeine per serving. No, we’re not kidding and no you don’t eat it. Caffeine can be absorbed through the skin. For maximum effect, ThinkGeek recommends that you build up a good Shower Shock lather across your entire body before rinsing!
(Emphasis mice)
Well, can it? The question got me looking. And lo and behold, shower shock is not necessarily a far fetched idea!
Feldman and Maibach. “Absorption of some organic compounds through the skin in man” The Journal of Investigative Dermatology, 1970.
Have you ever wondered whether aspirin could be absorbed through the skin? What, you haven’t tried rubbing some salicylic acid on your scalp for a headache?
Perhaps you haven’t, but it does make you wonder how many compounds can be absorbed through the skin. We generally think of our skin as a relatively impermeable barrier. And indeed it is impermeable to most inorganic compounds (as long as they are larger than 40 nm, which is very small indeed). But what about organics? We are exposed to lots of organic compounds all the time, from phenols (which include things like BPA, but which usually cause me to think of carbolic acid) to nicotinic acid (not nicotine, just sounds like it, and usually refers to niacin, an essential vitamin) to…well to aspirin! And of course, there is caffeine.
The authors of this study wanted to look at the absorption of various organic compounds through the skin. They took subjects (no note of who the subjects were, I keep wondering if the poor dudes were just using their own, highly abused forearms), and spread on 4 micrograms/square centimeter of skin of various organics, including nicotinic acid, phenol, caffeine, salicylic acid, 2,4-dinitrochlorobenzene (which can be used to diagnose immunocompromised patients, but which can also cause one heck of a skin rash for a poor volunteer), cochicine (used to look at mitosis), and thiourea (related to urea and primarily used in textile processing and silver polish).
Each compound was first radiolabeled with carbon14, and then spread on the forearm. The poor volunteers could not wash it off for 24 hours, and had to send all their urine to the clinic for 5 days. The authors then looked for the presence of radiolabeled compounds in the urine, which could determine whether the compound got into the skin and then into the bloodstream, eventually to be peed away.
So where do we end up with caffeine?
Pretty up there! The authors were able to find almost 50{9f43b4361d9a125bc126dd2a2d1949be02545ec69880430bc4fed2272fd72da3} of the applied caffeine in the urine, most of it coming out during the first 24 hours after application. The only other compound that did better was 2,4-dinitrochlorobenzene, while nicotinic acid came in very low, and urea worst of all (so, should you ever REALLY want you some urea…well don’t bathe in it).
While the study was being done to look at absorption of related compounds in the skin, the net result answers our question: will shower shock work? And the answer? Well, it probably DOES get some caffeine into your system. If you keep it on your skin and don’t wash it off. Though considering each “dose” is around 200 mg, a simple lather might give you a small dose.
But then there’s the bigger question: does the dose of caffeine in the shower shock soap have any real effect? What kind of blood levels do you end up with? Is it anything like a cup of coffee? Or is it something that the most caffeine-hardened of us (and thus, those most likely to buy the product) will brush off without noticing? From the reviews, it looks like it may just be a gimmick. But I would like to know just how much is getting in there per amount of time spent showering. Detectable blood levels at all? Shower Shock! I would like MOAR SCIENCE PLEASE! 🙂
Feldmann, R., & Maibach, H. (1970). ABSORPTION OF SOME ORGANIC COMPOUNDS THROUGH THE SKIN IN MAN. Journal of Investigative Dermatology, 54 (5), 399-404 DOI: 10.1111/1523-1747.ep12259184
