aren’t all the soaps antibacterial? How come some soaps (e.g. Dove) don’t mention anything about its antibacterial properties?


aren’t all the soaps antibacterial? How come some soaps (e.g. Dove) don’t mention anything about its antibacterial properties?

In: 149

Antibacterial means *kills* bacteria. And, at least in some jurisdictions, you need to actually to lab testing to prove that before you can make an anti-bacterial claim.

Removing bacteria (which all soaps can do) isn’t killing them, so doesn’t necessarily count.

All soaps have the property of weakening bacterial cell walls, and washing microbes off surfaces, but in terms of a legal definition they don’t hit that 99.9% kill rate that’s considered antibacterial. Soaps with additives such as triclosan and the like do generally kill at a much higher rate, but they come with their own issues such as breeding resistance in the surviving populations of microbes.

So in practice anti-bacterial soap is regular soap with one of these additives specifically designed to be antimicrobial. Such additives might also leave a residue that has the property of temporarily halting bacterial growth, so-called bacteriostatic action.

Yes, soaps are inherently antibacterial. They can disrupt the cell membranes of bacteria, which kills them. I’m not sure of the statistics there on % killed as a function of time, but you do need some contact time to see a big reduction.

Some soaps add one or more ingredients specifically to target killing bacteria. I think the presumption is that they’ll kill of a higher percent at shorter contact time, although I believe the evidence for that is shaky at best.

Washing your hands with soap *does* kill bacteria present, however that doesn’t make the soap antibacterial. Soap works by forming a complex with the plasma membrane of germs, and ripping them open as you add mechanical action and friction. This works for all germs, and is not something pathogens can build an immunity to!

Antibacterial means that if you apply soap directly to the germs, like on a petri dish, it will kill the germs or stop them from growing. Soap does not do this, as you need a lather composed of soap and water plus the mechanical action I mentioned previously to cause the membranes to rupture. This is why soaps sanitize things but are not antibacterial!

There are basically two ways that we can kill bacteria with chemicals.

The obvious way is by introducing a chemical that physically damages the cell. High concentrations of salt or alcohol will pull all the water out of cells and kill them. Soap will dissolve cell membranes and kill them. From that perspective, all soaps are “antibacterial.”

The other way is to take advantage of “programmed cell death”. Many cells (including many bacteria) have a mechanism to self-destruct when they get the proper signal. That’s “normally” invoked when killing off some cells is beneficial to the larger community of cells. “Antibiotics” trick cells by sending those signals. The problem is that cells eventually “learn” to ignore them. (“Learn” is actually total BS here. What’s actually happening is that not all cells pay attention to the kill signal reliably and when all the other ones die out the population evolves to one that consists entirely of bacteria that ignore the kill signal. But it looks like learning at the population level)

Typically a soap labeled “anti-bacterial” will have some amount of the latter chemicals in it.