Why don't antiseptic agents kill 100% germs?

Question

I've seen innumerable antiseptic, mouthwash, handwash advertisements that claim to be able to eliminate as much as 99.9% of all germs over a surface...but why not the remaining 0.1% (i.e- why can't they eliminate all germs)? Being a student of Biology, I can tell that the term "germs" is crudely defined. I would prefer to use "pathogens" (less ambiguous), and I suppose the guys that market these products have (roughly) the same idea in mind. Pathogens normally include bacteria (monerans), protozoans, fungi and viruses... so I guess these are the "germs" they're talking about. Why is it that these (commercial) products can't eliminate 100% of all pathogens? Is this due to the inability of antiseptics to act on a particular (class of) organisms? If so, what's the problem there? Or is it because, the guys who market stuff like this assume an arbitrary amount (0.1%) of the pathogens present on a surface (say, the human hand) is located in microscopic niches that are inaccessible to the antiseptic solution? (**If** it isn't possible to provide a blanket statement in this regard, use of *Listerine* as an example will suffice) In other words: Is an antiseptic's inability to eliminate 100% of all germs due to its "chemistry", or is it due to physical factors? Also, Do Antiseptics/mouthwashes/handwashes even kill 99.9% of all germs in the first place? Or is it (as I strongly suspect) an example of marketing fraud?

Answer 1

This is due to the effectiveness of the testing methods utilized for identify bacteria. They way the tests work is a swab is taken from a surface that has been treated with antiseptic and placed into media which is serially diluted and plated on agar. When an agar plate comes back clean, it can not be said to have no bacteria because there is no way to confirm this result.

As to your second question, it is scientifically proven that antiseptics/mouthwashes/handwashed kill/reduce the number of germs. If you are interested, there are at-home projects that you could do to confirm this for yourself.