We should add that soapy water does not kill the bacteria, but rather makes it impossible for them to adhere to anything, so they get washed down the drain.
Washing bacteria down the drain is certainly the primary purpose for using soap, by far, but surfactants like soap also kill a few bacteria by lysis (disruption of the cell membrane, causing the cells to rapidly swell with water and burst). In practice, this is so minor it’s not worth paying attention to: bacteria have a surrounding cell wall made of a sugar-protein polymer that resists surfactants (among other things), dramatically slowing down the process to the point that it’s not practical to make use of it.
(Some bacteria are more vulnerable to surfactant lysis than others. Gram-negative bacteria have a much thinner cell wall, which is itself surrounded by a second, more exposed membrane. But gram-positive bacteria have a thick wall with nothing particularly vulnerable on the outside, and even with gram-negative bacteria the scope of the effect is minor.)
In practice, the big benefit of soap is (#1) washing away oils, especially skin oils, and (#2) dissolving the biofilms produced by the bacteria to anchor themselves to each other and to biological surfaces (like skin and wooden cutting boards). Killing the bacteria directly with soap is a distant third priority.
For handwashing, hot water is in a similar boat: even the hottest water your hands can stand is merely enough to speed up surfactant action, not to kill bacteria directly. For cleaning inanimate surfaces, sufficiently hot water is quite effective at killing bacteria, but most people’s hot water only goes up to 135°F or thereabouts, which is not scaldingly hot enough to do the job instantly.
For directly killing bacteria via non-heat means, alcohol and bleach are both far more effective than soap. Alcohol very rapidly strips off the cell wall and triggers immediate lysis, while bleach acts both as a saponifier (it turns fatty acids into soap) and a strong oxidizer (directly attacking the chemical structure of the cell wall and membrane, ripping it apart like a rapid-action biological parallel to rusting iron).
Fun trivia: your hand feels slippery or “bleachy” after handling bleach (or any reasonably strong base) because the outermost layer of your skin has been converted into soap.
I formulated this hypothesis on my own, but I have not seen evidence to back this up. I think a misunderstanding of this process has lead to the profusion of anti-bacterial soaps, which may be breeding hard-to-kill bacteria.
Those who are concerned may be interested to know that Ivory Liquid Hand Soap (and, in all the stores I’ve visited lately, no other) is a brand of liquid soap which contains no antibacterial ingredients.
Furthermore, it at least used to have a slogan like “so gentle you can even use it on your face” — and it does not have the warning “keep out of eyes” that, as far as I know, all antibacterial soaps have — and I do in fact use it as a face and body wash.
We should add that soapy water does not kill the bacteria, but rather makes it impossible for them to adhere to anything, so they get washed down the drain.
Washing bacteria down the drain is certainly the primary purpose for using soap, by far, but surfactants like soap also kill a few bacteria by lysis (disruption of the cell membrane, causing the cells to rapidly swell with water and burst). In practice, this is so minor it’s not worth paying attention to: bacteria have a surrounding cell wall made of a sugar-protein polymer that resists surfactants (among other things), dramatically slowing down the process to the point that it’s not practical to make use of it.
(Some bacteria are more vulnerable to surfactant lysis than others. Gram-negative bacteria have a much thinner cell wall, which is itself surrounded by a second, more exposed membrane. But gram-positive bacteria have a thick wall with nothing particularly vulnerable on the outside, and even with gram-negative bacteria the scope of the effect is minor.)
In practice, the big benefit of soap is (#1) washing away oils, especially skin oils, and (#2) dissolving the biofilms produced by the bacteria to anchor themselves to each other and to biological surfaces (like skin and wooden cutting boards). Killing the bacteria directly with soap is a distant third priority.
For handwashing, hot water is in a similar boat: even the hottest water your hands can stand is merely enough to speed up surfactant action, not to kill bacteria directly. For cleaning inanimate surfaces, sufficiently hot water is quite effective at killing bacteria, but most people’s hot water only goes up to 135°F or thereabouts, which is not scaldingly hot enough to do the job instantly.
For directly killing bacteria via non-heat means, alcohol and bleach are both far more effective than soap. Alcohol very rapidly strips off the cell wall and triggers immediate lysis, while bleach acts both as a saponifier (it turns fatty acids into soap) and a strong oxidizer (directly attacking the chemical structure of the cell wall and membrane, ripping it apart like a rapid-action biological parallel to rusting iron).
Fun trivia: your hand feels slippery or “bleachy” after handling bleach (or any reasonably strong base) because the outermost layer of your skin has been converted into soap.
I formulated this hypothesis on my own, but I have not seen evidence to back this up. I think a misunderstanding of this process has lead to the profusion of anti-bacterial soaps, which may be breeding hard-to-kill bacteria.
Those who are concerned may be interested to know that Ivory Liquid Hand Soap (and, in all the stores I’ve visited lately, no other) is a brand of liquid soap which contains no antibacterial ingredients.
Furthermore, it at least used to have a slogan like “so gentle you can even use it on your face” — and it does not have the warning “keep out of eyes” that, as far as I know, all antibacterial soaps have — and I do in fact use it as a face and body wash.