what is the ingredient added to soap that makes it anti-bacterial?
In: Chemistry
The simplest soap is water, oil and lye. It is the lye that is antibacterial, it is a very strong base so acts to chemically tear apart biological cells.
Our skin has layers of dead cells so the soap doesn’t damage us. But if you get soap in a cut, you can feel what it is like to have your cells being destroyed.
A lot of modern soaps like dish soaps don’t have lye. Lye is also neutralized during the soap making process.
There’s a few things in play though
The soap has certain molecules called surfactants in them (there are many chemical molecules that are used for this purpose). These have a side that love water and a side that doesn’t like water.
The surface of bacteria don’t love water either. Like attracts like and the side of the surfactant that doesn’t like water draws the bacteria towards them. This lifts bacteria from your skin. Once they are free, the surfactants keep attaching and traps them in a tiny drop.
The double whammy is the simple movement of your hands rubbing together also tears bacteria apart. Which makes washing your hands with soap very effective at removing bacteria
I think you’re asking about the soaps that are sold specifically as antibacterial, like they say “kills 99.9% of common household bacteria” or something like that? Like others said lye in soap does act as an antibacterial agent but those soaps have actual antibiotics (drug type) added to them. The antibiotic drugs we use are really just a molecule that we discovered somehow interferes with bacteria and kills them.
Since the antibiotic is just some small molecule, you can just put some of it in the soap and it will dissolve. That’s literally it. To make those claims and test for safety they would test lots of different doses of antibiotics in the soap, test it on a surface and take samples before and after to see how many fewer bacteria are in the soap to find the correct concentration of antibiotic to use.
Most anti-bacterial soaps are made with alcohol. They’re antibacterial the same reason hand sanitizer works.
Alcohols kill bacteria
Microbiologist here: most soaps (like Dial) that are labeled as “antibacterial” *do* contain a biocide, Benzalkonium Chloride, typically. This compound helps to break up outer lipid layers of microbes. It isn’t an “antibiotic” in the sense that something like penicillin is (which uses chemicals to disrupt the biological machines that form the cells), but it has a similar effect. It also has surfactant activity, which adds to the purpose of the soap – to lift dirt and gunk, including microorganisms from other surfaces like your skin. Of the various compounds that does this, BC is reasonably effective without being terribly toxic to you (and is inexpensive).
To use an analogy, using BC is like hurling a stone at a brick wall (the microbial cell) whereas using an antibiotic like penicillin is like hiring a secret agent bricklayer who is intentionally really bad at building brick walls. Oops your castle wall fell, sorry king!
The chemical is simply added to the soap mixture.
Personally, I don’t use these kinds of soaps, regular soap is good enough, but it’s reasonable to see them in places that are germ-prone, like a hospital or daycare center.
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