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I have read that general soap can kill bacteria by opening holes in the bacterial membrane.

http://questions.sci-toys.com/node/90

However, I found some articles as well saying that it cannot.

http://goaskalice.columbia.edu/answered-questions/does-soap-kill-germs

There seems split answers among experts, so I would like to know which one is correct.

Could anyone advise me?

Thanks.

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    $\begingroup$ If you look all the way down at to bottom of that ask Alice post, you will see that it was originally posted in 2001. Many major health organizations have done efficacy studies since then and have weighed heavily in favor of the use of regular soap over antibacterial. However if the choice is antibacterial or not washing your hands, then go with the antibacterial. $\endgroup$ – AMR Oct 25 '15 at 13:48
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Soap kills nearly all the bacteria it comes into contact with by dissolving the bacterial membrane. Some viruses with protein coats can resist soap, but many viruses have similar membranous coats (like HIV) and are usually disrupted by soap. I'm sure it washes some away too, but to say they don't kill bacteria is misleading. In the end, though, they are gone.

Antibacterial soap with triclosan does not kill bacteria on contact and are no more effective than if they had no triclosan at all. That's actually a good thing since really using an antibiotic would probably accelerate antibiotic resistant bacteria which is a serious - probably catastrophic public health failure. A recent study showed that killing bacteria by soaking with triclosan took 9 hours to start showing an effect.

To achieve full sterility, surgeons bathe their gloves in iodine (see details in the comments below) and their instruments will be sterilized by heating them beyond the boiling point in an autoclave under pressure. That's useful when you are breaching the skin in surgery, but the skin needs some bacteria to be healthy long term and works well to fend off bacterial infections.

Your confusion seems to come from finding a page full of errors. Alice didn't really do her homework.

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    $\begingroup$ In a surgical setting, isn't the iodine use in the form of Betadine (povidone-iodine)? Also, Chlorhexidine is use a lot as a patient preoperative prep and also a wound cleanser. $\endgroup$ – AMR Oct 25 '15 at 13:39
  • $\begingroup$ @AMR you clearly know more than I - happy to accept these amendments! $\endgroup$ – shigeta Oct 26 '15 at 14:44
  • $\begingroup$ "Soap kills nearly all the bacteria ... by dissolving the bacterial membrane." I thought soap only worked to dissolve lipids. Aren't bacterial cell walls are made of peptidoglycan (non-lipids)? $\endgroup$ – 425nesp Apr 1 at 19:50
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Soap is a detergent. It actively emulsifies the bacterial membrane, thus killing them by breaking this membrane. So yes, soap kills bacteria. Some bacteria are more or less resistant to this depending on the constituents of their lipid-bilayer membrane.

The reason why soap doesn't hurt your own cells is that for the most part, your outer skin layer is comprised of dead cells that have numerous cross-linked keratin filaments mixed with oils from your sebaceous glands that provide a nice nearly airtight, watertight barrier.

Excessive hand-washing or washing hands with stronger detergents can actually get rid of this protection and break down the barrier mentioned in the prior paragraph, leading to dry and cracked skin.

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  • $\begingroup$ How does the soap get passed the bacteria capsule and cell wall to the bacteria's cell membrane to emulsify the membrane? The capsule and wall are not made of lipids. $\endgroup$ – 425nesp Apr 1 at 21:00
  • $\begingroup$ Are you confusing a viral capsid coating made of proteins with bacterial cell membranes? Some bacteria, under stressful environmental conditions can also encapsulate, but most of the bacterial we pick up from the environment and food are not encapsulated. $\endgroup$ – akaDrHouse Apr 3 at 3:00
  • $\begingroup$ I'm looking at the gram-positive bacterial cell here. en.wikipedia.org/wiki/Bacteria#Cellular_structure It seems like at least that bacteria has a capsule and also a cell wall, then a cell membrane. Ah, but maybe where I'm confused is that not all bacteria are structured like that? $\endgroup$ – 425nesp Apr 3 at 16:47
  • $\begingroup$ No, you aren't confused. Gram negative bacterial have two "lipid bylayer membranes (inner and outer)", but also a peptidoglycan layer between. That layer between is much harder to disrupt with detergents, and thus they present more of a problem! $\endgroup$ – akaDrHouse Apr 3 at 19:59
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Generally, the goal for using non-antimicrobial soap is simply to pick up and remove organisms and dirt from our skin. This is achieved first by the soap chemically bonding to certain molecules (i.e. oil or lipids). Second, friction from rubbing mechanically and rinsing with water pick up and removes the soap and chemically bonded particles. Thus, the more soap and the longer the hands are rubbed together, the less oil and microbes left on your hands.

For a more scientific answer:

Soap is a detergent, meaning one side of the molecule is hydrophilic (likes water), and the other is hydrophobic (likes oil). Cellular membranes are also made out of a dual sided hydrophobic and hydrophilic molecule called a lipid. The soap solvates the hydrophobic parts of the lipid cell membrane, and you're left with a mixture of lipids & oils suspended in the soap. These are washed away when you rinse with water (imagine how cooking oil floats on top of water).

For another (longer) response to this question see here.


Comments on website credibility:

I'll also comment that at any point that you do an online search, you REALLY need to pay attention to the source of the information you're looking at. The internet is crawling with misinformation and inaccuracies -- often represented as fact or even presented by a so-called 'expert'! Typically, .edu websites (from academic institutions) are MUCH MUCH more trustworthy than .com, .org, etc. because they typically originate from some kind of peer-review or life-long study of a topic.

Be cautious, however, that you don't end up on a .edu page that contains a student's (or other non expert's) thoughts/opinions/or (possibly wrong) response to a question. Further, unfortunately it's not always this simple, as .org or .com info isn't necessarily wrong.

If you want to increase your odds of finding the most accurate information, go straight to the peer-reviewed literature (start a search here). If this is too daunting a task or if you can't find what you're looking for, then I'd suggest focusing on .edu websites for info. You can use the "site:" operator in a Google search to specify a domain -- specifically, if you’re looking for high-quality references, you could use site:.edu to only pull up results from .edu domains.

That being said, I think it's clear that your first link is not nearly as trustworthy as your second, and in this case can be dismissed as internet misinformation.

Hope this helps!

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    $\begingroup$ Great comments on the credibility of that website. It was horrid. $\endgroup$ – akaDrHouse Oct 24 '15 at 16:53
  • $\begingroup$ Please upvote the response then, so that more people are drawn to it. Thanks! $\endgroup$ – theforestecologist Oct 24 '15 at 17:12

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