Another look at soap and science


Earlier today, guest blogger Sean Bonner posted a study that he said supports his decision to live a soap-free lifestyle.

Now, I don't really care too much about the soap/no soap debate one way or the other. Although I have not personally met him, Xeni assures me that Mr. Bonner really is pleasant to be around, without any funky odors to him. And, regardless of his success, I'm not likely to give up things like shampoo and apricot scrub anytime soon, due to my own personal experiences managing my hair and skin.

But, I thought it would be interesting to do a Google Scholar search, and try to get an idea of what the scientific literature, as a whole, says about the value of soap. Or lack thereof. Before you read on, please note that I'm not sure how applicable this information will be to the specific soap/no-soap partisan divide here on BoingBoing. Most of the research I found was either studying handwashing practices among health care workers, or sanitary precautions in parts of the world that have ongoing problems with some nasty communicable diseases that aren't really a big deal in the United States and Europe.

That said, here's what I found:

•So, first off, the study that Sean Bonner cites isn't necessarily a great argument for the superiority of water-alone washing. Only about 40% of healthcare workers comply with handwashing guidelines (yipes, right?), so people are constantly looking for ways to reduce disease carrying. The idea behind this study is that, even if the soap-and-water method works best, it doesn't help much if people don't do it. If they will use a squirty gel thing, even if it it kills fewer germs than the soap, maybe you're still better off in the long run. The goal wasn't to prove what cleaning option was best, but to see how well the non-washing-based options did, with the idea of choosing one to use as a realistic alternative to handwashing. You'd want to set up a different sort of study to test the question of whether people are better off without soap.

This study ran two sets of trials using a bacteria in one and a virus in another, with 14 different cleaning options, including the two controls—water alone, and soap and water. With the virus, after 10 exposures, water alone was killing the most bugs, followed closely (closely enough that you can't really say water alone was absolutely better) by plain soap and water. But with the bacteria, the situation was different. After 10 exposures, water and soap-and-water were again running neck and neck, but they were both at the bottom of the pack. Soap with 2% chlorhexidine gluconate won the day.

Basically, this one study doesn't tell us much about soap vs. no soap.

• I didn't find any studies that directly compared whether washing with soap or washing without soap killed more germs. Doesn't mean they aren't out there. This was kind of a cursory scan. But it's safe to say that this question isn't of the utmost importance to most public health researchers.

• One of the reasons healthcare workers don't wash their hands as often as they should is because of soap-induced irritation of the skin. There are lots of studies addressing this problem. But, again, healthcare workers are outliers. If you aren't a healthcare worker, and you're washing your hands as often as they are—often enough to get serious skin irritation—you might want to try less frequent washing before shifting toward giving up soap entirely.

• A systematic review of the literature on handwashing and diarrhoeal disease (meaning that the researchers reviewed and compiled data from every study done in a specific way, on this specific topic) found that "washing hands with soap can reduce the risk of diarrhoeal diseases by 42-47% and interventions to promote handwashing might save a million lives." Again, bear in mind, this is talking about developing countries, and it doesn't tell you whether washing without soap would have done better. But it does seem like there is some value to soap.

• I saw a study called "Soap May Seriously Damage Your Health", and thought I'd hit a jackpot. Turns out, it's actually about soap operas. Apparently, there's a correlation between the popularity of a specific suicide method, and whether a TV character has used that method to kill themselves recently.

• Not washing your hands after using the bathroom, and not washing dishes and utensils thoroughly, has been associated with an increased risk of diarrhea among American wilderness hikers. One study specifically called out the use of soap as a protective behavior. Apparently, previous research has shown that you need to use some kind of rubbing agent (soap, ash, or dirt, in the case of campers and backpackers) if you want to actually get fecal matter and the contaminants it carries off of your skin. Which, you know, you do.

Bottom line: I can't conclusively say whether soap is better than no soap. And it seems like the no-soap option is significantly better than no washing at all. But there is, at least, some research out there suggesting that soap is better—in certain situations—at preventing diarrhea.


  1. As someone with mild OCD, I say with only the slightest hint of joking that skin irritation is kind of the *point*. If your skin’s not red and raw, you’re not doing it right or often enough.

  2. Ewww. Gonna have to remember this guy’s name so if I ever meet him I know not to shake his hand.

    Sean Bonner sounds like a Luddite.

  3. I spent some time working on a control system in a food factory in the UK. There were knee-operated handwash stations dotted around the place, and the rule was that every time you passed one, you had to wash your hands thoroughly with soap. Everyone did, as far as I could tell. The stations were in the main walkways, so people could see if you ignored them, and there were no back ways or shortcuts. There were times when I’d walk past one, wash my hands, realise I’d forgotten something in the office, have to go back, then come back and have to wash my hands again. There was also knee-pumped lotion dispensers as well. It was all well accepted and normal behavior for the workers in the factory.

  4. Great post! There’s also a correlation between handwashing with soap (often written HWWS in medicine) and lower rates of respiratory disease. My Wikipedia buddies have more:

    Until today’s post, Sean’s claim seemed to be mainly about not stinking. I am willing to accept that possibility. Bringing in the question of efficacy re: hygiene changes the game and veers the discussion into much more serious issues. The article Sean cited is definitely not the best example to support his claim. I think I’ll err on the side of Joseph Lister, personally.

  5. As a health care worker (I’m Director of Environmental Service at an 80-bed nursing home), I’d like to point out that the primary reason for encouraging people to wash their hands frequently isn’t so much to prevent them getting sick as it is preventing them from getting others sick.

    Every doorknob, every light switch, every hand rail, every dinner tray, every TV remote, every thing you touch can carry whatever it is you DIDN’T wash off of your grubby little paws.

    We deal with CDiff, MRSA and worse, in a population whose auto-immune system isn’t necessarily up to snuff. I wash my hands early and often.

    When at home, I use Grandma’s Lye Soap, with no detergent and no fragrance. I see it as a compromise and it works.

    I do remember when my brother went the no-soap route, back in the hippie days. He smelled like a hippy. I introduced him to Dr Bronner (ALL ONE! OKAY!).

  6. I was under the impression that the no-soap posts were more about *showering* with soap as opposed to not handwashing with soap? Maybe I haven’t been paying close enough attention after all… But no soap on the rest of your body vs. no soap when you wash your hands seem two completely different things to me.

    1. This is where the questionable applicability kicks in. I didn’t see any studies on showering without soap.

      1. right. but just to be clear, doesn’t bonner’s original post specifically state that he washes his hands with soap?

    2. You’re right, surreality, this is all a little beside the point Sean was making in his posts. As he stated originally, and again in comments, “of course I still wash my hands with soap”.

      Still, for anyone considering trying the soapless shower and deodorantless experiment themselves, it’s prob’ly worth bearing in mind that the experiment does not include forgetting to wash your hands after using the toilet.

      I don’t think they’re suggesting, either, that you get cleaner without soap, merely that what’s marketed as soap these days is putting a lot of unnecessary stuff into your pores, which isn’t necessarily helping you clean, and may, in some cases, be hampering the effort.

    3. The no-soap posts USED to be about showering without soap, but the most recent post cited a paper specifically regarding hand-washing, and grossly misrepresented the contents of the paper.

  7. Could we dare maybe to just engage our chemical brains a bit? Bacteria and some viruses depend upon a phospholipid cell membrane to keep them together. Water with various solutes is what they live in. Soap is something that disrupts and solvates chemicals that are apolar and amphipathic by forming micelles with and around them. This will ruin any (non-ensporulated) bacteria’s good times.

    So seek ye studies, weigh the evidence, good for you-all! But as sure as oxygen is needed for combustion, soap will do a better job of killing bacteria than no soap.

    1. So seek ye studies, weigh the evidence, good for you-all! But as sure as oxygen is needed for combustion, soap will do a better job of killing bacteria than no soap.

      But what’s interesting is that the data really doesn’t support this. The studies Maggie cited showed no difference between water and water+soap in killing bacteria.

      But with the bacteria, the situation was different. After 10 exposures, water and soap-and-water were again running neck and neck, but they were both at the bottom of the pack.

      The only time it made a difference was in preventing diarrhea, where it was needed as a “rubbing agent,” and could be substituted with dirt. So there actually isn’t any study that implied that breaking bacteria’s phospholipid cell membranes had anything to do with getting rid of them.

      My guess is that, given the study that showed that soap+water was at the bottom of the pack along with water alone, regular soap simply isn’t strong enough to destroy bacteria’s cell membranes.

      1. My guess is that, given the study that showed that soap+water was at the bottom of the pack along with water alone, regular soap simply isn’t strong enough to destroy bacteria’s cell membranes.

        While the study seemed to zero in on the efficacy of soap re: killing bacteria, I didn’t think that was really the point of soap. As a surfactant (hydrophilic head/hydrophobic tail), soap lowers the surface tension of water increasing solubility of various “stuff” on the skin (including body oils). Then as the water/soap mixture is rinsed away, all the particulates suspended are rinsed away as well.

        Short version: Soap main function is to *remove* germs, not kill them.

  8. I started axing the soap when I shower at the start of this year without telling my girlfriend. Last night I asked if she had noticed a difference in how I smell. She said that the only thing she noticed was that my hair was softer, but nothing on the oder front. I’ve actually stopped using deodorant except for when I am working out (4-5 times a week) but I do shower afterwards before going back to work and have not received any complaints (the folks here would not be shy about saying something). So for me the no soap showering is working out well.

    Now the no soap policy is only being applied to my showering. If I am cooking or have used the restroom, you better believe I am using soap. Letting your body regulate oils and such is a whole different deal than killing pathogens which could wind up in what I am eating.

  9. Some rather interesting information regarding this subject can be found in Mary Roach’s excellent book Packing for Mars, specifically, in chapter 10. Being confined to a spacecraft, particularly one with no toilet or shower facilities, can present some real personal hygiene hazards! I wouldn’t want to spoil the fun of reading it, but… e coli migration, anyone?

    After watching a few of my friends deal with MRSA infections, you bet your bootie I wash my hands with soap.

    And, from personal experience, I can tell you that water alone just doesn’t cut it after a long, bath-free hiking or camping expedition… give me the soap, please.

  10. The thing is, soap never really added that much to washing with water. The studies you cited in support of soap didn’t study washing without soap.

    The original idea of handwashing, if you’ll remember, largely occurred when doctors didn’t wash their hands between the morgue and treating obstetrical patients and killed many women. The fix for that was hand-washing. They used water only, and it was very effective. Every study of which I am aware has supported the idea that tap water is as good or at least almost as good as anything else for getting rid of germs.

    Now, Sean wasn’t making a medical argument there. He was making an argument that “hey, this isn’t so gross, because after all there is very real evidence that in addition to not stinking, it also actually does get rid of the great majority of germs”. It’s a very sound argument.

    The medical argument, if one were to be made, also happens to be pretty sound. The other thing to remember is that, while many societies throughout history have had problems with sanitation, there are also some that haven’t. Romans were pretty decent, for example. They didn’t wash with soap. If anything, Mediterranean cultures washed with things like olive oil and maybe scraped it off.

    The whole reason that detergents are effective is that they bond with oil as well as water, allowing water to wash away oils. But applying more oils and scraping them off works just as well, perhaps better. And, as Sean has pointed out, it does not have some of the negative consequences such as drying the skin. Many studies have proven that dry skin (like you might get with a lot of handwashing, especially in winter with the lower humidity) harbors bacteria like nobody’s business. That soap can make this worse (that’s right, hand-washing can actually lead to more bacteria on skin and the need for ever-greater amounts of washing to get back to a baseline) has been commonly accepted for decades.

    There’s really no debate here worth having. Many cultures that don’t bath nearly as frequently as Americans have fine hygiene and health. Americans are neurotic about washing and soap, to the point that even the popular media comes back around to the point from time to time in comparing with other cultures. Usually the lack of support for quite so much washing, especially with detergents, is highlighted pretty well.

    One final example. Cookware. When you cook with cast iron, you don’t wash it with soap. You clean it with oil or you’ll ruin it. But guess what – it does get clean, and you’re going to heat it up pretty good when you cook again anyway. It works. But most people would rather use half a bottle of dishwashing liquid on nonstick pans, which could pretty well be gotten clean by rinsing immediately after using, and with far less effort.

    1. Every study of which I am aware has supported the idea that tap water is as good or at least almost as good as anything else for getting rid of germs.

      Really? Cite, please.

    2. Agree with most of what you’ve said. If anyone is interested, “The Dirt of Clean” is a book on the history of cleanliness (in the western world) that I found quite illuminating.

  11. Okay, as any handmade soapmaker can tell you, most modern bar and liquid soap sold in stores is not true “soap” but chemical detergents that are cheap and easy to produce for a mass market. So, yes, they are quite drying to the skin and irritate the mucus membranes, throw off your pH, strip off the “good oils”, etc., in some way because of the harsh chemicals involved. Sure, plain water by itself is going to leave your skin and hair feeling better than these detergents. I strongly urge anyone considering going “soap-free” due to skin irritation to first try using actual soap and see how that works.

  12. Big difference between using not soap for handwashing and not using it for showering or not using shampoo for washing your hair.

  13. I also dived into Google Scholar but did not find any recent papers comparing “just water” to anything else – admittedly I’m at home and I don’t have the same access to scientific journals that I enjoy at work, so my search wasn’t very productive. It doesn’t seem like the issue of “just water” vs “others” has received a lot of attention, and it would surely be interesting to see new research on this (also, the numbers in the paper that started all this seemed a bit low for the statistics).

    However, I did find the “Guidelines on Hand Hygiene in Health Care” issued by the WHO in 2009. This document states “While water is often called a “universal solvent”, it cannot directly remove hydrophobic substances such as fats and oils often present on soiled hands. Proper handwashing therefore requires the use of soaps or detergents to dissolve fatty materials and facilitate their subsequent flushing with water. To ensure proper hand hygiene, soap or detergent must be rubbed on all surfaces of both hands followed by thorough rinsing and drying. Thus, water alone is not suitable for cleaning soiled hands; soap or detergent must be applied as well as water.“. It then goes on to discuss the problems of contaminated water (another can of worms). And I find that’s enough for me.
    If a no-soap regime works well for some people, good for them!; my personal experience is that after a whole day of going to work, walking in the commercial zone of town, and especially being in places with lots of car traffic, my skin ends up covered with a film of hydrocarbon substances that water alone can’t remove.

  14. Also, if the Anon from the last post who asked about antibiotics is reading this thread as well, I put up a response on that last thread.

  15. One of the reasons healthcare workers don’t wash their hands as often as they should is because of soap-induced irritation of the skin.

    That, as it turns out, is mostly untrue. A few individuals will have sensitivities, but handwashing dermatitis is generally caused by not completely drying your hands every time that you wash. I worked in a hospital for decades. Infection Control has studied these things rather thoroughly.

  16. What about using ordinary table salt? It’s a good abrasive until it dissolves, it doesn’t remove oils from the skin, and it kills stuff.

  17. Soap is not very effective at killing germs, unless it has antibiotics in it. Instead, soap helps to dissolve dirt and oils, as well as the bonds that germs use to attach to things, to aid removal of the germs from the skin when rinsing with water. So I am not surprised that you found articles that indicated that soap was little to no more effective in studies testing how well it killed germs on a plate. If you don’t want to use soap when showering on your whole body, I understand. I personally feel you should keep washing your hands with soap, regularly.

    Note: IANTKoD (I Am Not That Kind of Doctor).

  18. Can we just split this up into a discussion of: handwashing after coming into contact with pathogens (which is, well, common sense); and not using body wash or shampoo?

    I really don’t see the correlation. I don’t use the stuff in the shower, and it’s sort of foolish for everyone to assume that means walking around with your hands covered in feces and Ebola.

  19. Here’s what I’d like to know – where can I get soap that is actually soap, and not detergents? I’ve got soap lite lately, but haven’t noticed a difference. I’d prefer to use something closer to, you know, real soap, instead of this new crap, but I have no idea where to find it!

  20. I work in the field of bone marrow transplant. Hospitals are very concerned, and rightly so, over antibiotic-resistant bacteria. Hospitals that have increase health care providers use of hand sanitizers and hand washing show a significant decrease in infections vs. hospitals that did not have this protocol.

    In transplant, patients lose their immune system for a while and any infection becomes life-threatening.

  21. If you read the Bonner’s article, you will see that he still washes his hands with soap. This fact makes this article rather pointless.

  22. Many commenters seem to forget that there are good bacteria and bad bacteria. The vast majority of bacteria are harmless, and maintaining healthy populations of friendly bacteria on our skin can help exclude the few that may cause disease. It’s called competitive exclusion.

    Don’t get the idea that using soap gets rid of all bacteria. Or that doing so is even a good idea. Our skin harbors a living ecosystem. Excessive use of soap can disrupt the community of good bacteria and create opportunities for the bad bacteria.

    One might be wise to use soap after using the bathroom when the risk of bad bacteria is greatest, and there is certainly good reason for medical staff to try to disinfect their hands before going into surgery.

    Reducing the use of soap, such as showering without soap, seems like a good way to get “clean” without unduly disrupting the community of good bacteria that should be nurtured, instead of persecuted.

  23. I remember a discussion from a college anthropology class of an African bushmen tribe (sorry, I don’t remember their name or know the PC term). The only detail that stuck with me was that they washed their hands each morning with ash and urine. The urine acted as an antiseptic and the ash served as an exfoliate.

    Anyone interested in upping the stakes in their self experimentation?

  24. Comment #30 from Anon was spot on.

    I find typical American thinking to be “kill all the germs”. However thoroughly cleaning a surface will only make a perfect growing place for any microbe without any competition. I.e. If you happen to get the bad one first it’ll flourish. However if the surface would be totally covered with harmless microbe flora then there wouldn’t be any easy way to the bad ones to grow. Competition between various strands would maintain the balance.

    Maybe we should try washing with buttermilk or yogurt instead :-)

  25. the way i do it is this:

    soap for my hands, and often. soap for bum and sometimes for my feet. nothing but water for showering and washing my hair.

    i also didn’t tell my partner and asked her two months after changing my washing habits. she had noticed a better smell, but didn’t think about an explanation before i told her.

    i use a piece of washcloth and a natural sponge when taking a shower and change them often. and

    i am used to having a sauna at least every two weeks. i run a sixmiler every week. i think i wouldn’t have dropped the soap without working out regularly.


  26. Univerity of Regensburg (Germany) actually did do a survey.

    They found that washing hands without soap (just water) is as good as not washing your hands at all. For good cleaning you need to wash with soap for at least 30 seconds. The temperature of the water didn’t seem to have any effect.

  27. So, the point of soap is to remove visible dirt/filth, if you have no visible dirt then yes washing with water is just as effective. However, as anyone with children or anyone who works outside will attest, hand washing without soap is pointless and stupid – incredibly tedious and time consuming (not to mention wasteful of water). Even hand sanitizers state you must remove visible dirt in order for them to be effective, again they don’t work if you don’t wash first.

    For those of us who wipe asses all day long (diapered), run after kids who play in dirt, who dig in dirt, who have reasons for having visible dirt (night dirt or otherwise) on our hands – soap is needed and serves a very specific and useful purpose. Hell, soap with pumice in it (Lava soap) has a specific purpose too – again to remove visible filth. Moreover I sure as hell wouldn’t want my dairyman washing with plain water…

  28. A fine point: handwashing isn’t really about killing pathogens as much as it’s about getting them off your hands and down the sink drain. Soap and detergents help get them off your skin by making the water wetter, but they aren’t bactericidal to any useful degree.

    Neither is hot water. Lots of people believe that hot tap water kills germs, but it would have to be really, really hot (hotter than its sea-level boiling point in fact) to be effective in that way.

    recovering RN

  29. Even if you believe in unicorn warlocks and think soap is the only possible way to get clean — which is fine, don’t let me take that away from you — you’re still probably using way more than you need. Very quickly, you’re just dumping chemicals on yourself for the pure glee of it.

    We’ve all stretched the bottom of the shampoo bottle into a veritable bottle’s worth of shampoo solution: We all know the truth.

  30. Right, that’s what I was saying. Sorry it wasn’t clear. My point was that biological explanations of phospholipid cell membrane were probably incorrect, and that soap was just a better remover of stuff from your hands than plain water.

  31. What irks me most about this post and many of the responses is that it seems scientific, but its just a bunch of unwashed hand waiving rhetoric.

  32. I don’t use soap or shampoo when I shower. I wash my hands with soap after mucking out the pigs’ shed or the chicken coop. Soap is an effective method of dealing with pathogens, and specifically on the hands, which can transmit pathogens to the mouth, nose, etc… But my body is not generally covered with pathogens that need “dealing with.”

    You can’t apply sanitary standards of healthcare workers to everyone else because they are especially exposed to pathogens and because the risk of cross-contamination is much higher due to how many people they come into contact with. You can’t apply the sanitary standards of food-industry workers to everyone else, again, because the downstream risk is so high. If you’re in one of these especially sensitive areas, higher sanitary standards are necessary.

    But for most of us, the amount of pathogens to which we’re exposed on a daily basis does not call for specific antiseptic treatment. IMO–I have no studies to back that up. The problem, I think, is when we start treating all potential pathogens as undesirable, using soap everywhere, and then anti-bacterial soap, and then hand-sanitizer, and then…

  33. I’ve been wracking my brains trying to figure out when the photo above was taken. Usually, I can guess within a few years when I see a picture; I can usually place the decade.

    But this looks like a weird combination of the 1920s, 1950s and ’70s.

    When the heck was it taken???

  34. I think the only thing you can really get from all this is that a. soap and water is sometimes necessary for washing, and b. YMMV. How many of us are going to go up to someone who smells funky and ask how recently they bathed, and if they used soap, deodorant, etc.? That’s just asking for a pop in the nose.

  35. I just came out of the toilet and then read this. Now I can’t help but smell my fingers and think “Christ, what an asshole”.

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