Friday Weird Science: Need more caffeine? Rub it in.

Feb 22 2013 Published by under Friday Weird Science, Uncategorized

Today's Friday Weird Science was inspired by @TruffledSquirrel, Who sent me the following tweet.

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?

caffeine skin1

Pretty up there! The authors were able to find almost 50% 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

12 responses so far

  • biochembelle says:

    My inner chemist notes that aspirin is actually acetylsalicylic acid - not much difference in absorption, but different effects :)

    I had seen caffeine soap on ThinkGeek and had assumed it was just a gimmick. Curiosity got the better of me after reading your post. Seems some caffeine is absorbed rather quickly, and more so if your follicles are open. So I suppose if you don't mind standing around covered in soap for 5 min, you might get a little boost... but I think I'll just stick to coffee.

  • louis roberts says:

    make a pot of very strong coffee.
    add to it an emulsifier.
    add to it your favorite oil(s).

    have your partner rub you down in it.
    the trick is in the emulsifier.

  • laurenkwolf says:

    It's funny--I had just been contemplating caffeinated shampoo and wondering some of the same things as you. I saw a commercial on TV for Garnier Fructis. One of their new shampoos has "energizing caffeine" in it to strengthen hair and reduce breakage of strands. Seemed pretty far-fetched to me, considering that caffeine binds to adenosine receptors in the body to exert its influence. But I had come across the same paper @biochembelle did. Perhaps we need an expert to weigh in?

  • Len Littenberg says:

    This sounds interesting but I like coffee, I'll stick to the traditional method. I can't help but wonder if you meant "emphasis mine", saw the typo, and left it. I kind of like the idea of mice running amok highlighting pertinent phrases.

  • Someone just explained to me, like an hour ago, that you can make your own bath scrub (like a salt scrub or sugar scrub) from used coffee grounds. Seems like an interesting idea.

  • Agesilaus says:

    Dimethyl Sulfoxide is well known to be absorbed thru the skin and supposedly carries other organics with it. If they are mixed with the DMSO. After a skin application you'll soon be tasting garlic which is the flavor of DMSO apparently.

    As for topical aspirin, for many years there was a topical product containing Aspirin. The company producing it widely advertised it as an agent to relieve muscle pains.It vanished from the market, I seem to recall they had a problem with the FDA. But searching on "topical aspirin" shows that some forms of the material are still available.

  • Jessica B says:

    I think "emphasis mice" might be my favourite typo ever.

  • highdesert says:

    If you're going to go transdermal, one of the caffeine patches (caffederm, etc.) is probably a more effective delivery mechanism than is the soap. Of course, why go to the trouble when you could just drink coffee, nectar of the gods, instead?


    Hi There. DMSO is absorbed thru the skin almost instantly, carrying aspirin or other suff along with it, BUT, DMSO causes Glaucoma and other nasty conditions so DO NOT try it for caffeine.

  • Rolf Degen says:

    Here in Germany, caffeinated shampoos are all the rage. And it is not for the puported "energizing caffeine" effect. German scientists have proved that caffeine blocks the effect of testosterone in the scalp. As bald heads are existing allmost exclusively in men, the anti-tesosterone effect is supposed to combat baldness. The caffeinated shampoos are marketed this way, as anti baldness shampoos. And people, what shall I tell you, this stuff makes my hair strong! This stuff is good!

  • Amanda says:

    I'm a defense lawyer who works on a drug/dui court team. We warn our participants that alcohol can be absorbed through the skin from things like purell and cologne, and I've always wondered just how much contact they'd h positive have to have for it to show up in a per test.

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