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Suppose a device was able to make water remove 99.99 % of bacteria on the incident surface (assuming that the water is germicidal by itself, whatever the reason – e.g. by means of an additive which would have no other consequence).

Would it be beneficial or harmful to regularly shower with such water ?

The question is specifically about the whole body, as opposed to mere hand-washing, for which I think the benefits in terms of infection reduction are not disputable and would overcome any potential harmful effects on the skin microbiota.

NB : This is not a rhetorical question, some people actually claim their device is able to do so (I don't want to go into details in this particular question, but this cross-SE related question may help its understanding : how much does sprayed water remove bacteria ?).

  • Welcome to HealthSE! Please take the tour and read the help. And please clarify: the water is not germicidal but germ-reduced before it is used? – LаngLаngС Jan 10 '18 at 19:36
  • Tour and help are there to guide new users into the site. How to ask being also important… Everyone should read those at least once. – Thx for the clarification, it's the the other way around from what I thought. – Please add those updates via an edit into your question; comments are volatile and may disappear at any time. – LаngLаngС Jan 11 '18 at 0:41
  • Justifications of downvotes are welcome... – Skippy le Grand Gourou Jan 11 '18 at 6:40
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Routinely killing your skin microbiota is indeed a bad idea. Using "germicidal water" as the usual shower water would do just that and very likely cause more problems than it should like to solve.

However, looking at the "device", a seemingly simple shower head's description:

  • Transforms tap water into energized & ionized water. Get unlimited ionized water from faucets .
  • Sanitizing* ability to help remove and separate harmful materials
  • 3rd Prize in 2010 Korean Invention Patent Conference with Korea & World Patent
  • Easy to install on all faucets, No Maintenance Costs, Semi-permanent use
  • Helps remove free radicals, rancid smell, dirt, pollutants, skin problems

Multi-Ionizer SH is an anion high pressure handheld shower head. The energized and ionized water effectively removes dirt, oil, dust, contaminants and oxidized materials. It helps to clean and energize your whole body and removes dead skin cells. It produces more than 200,000 negative ions per cc while Yosemite waterfall produces 100,000 anions per cc. You can enjoy highly refreshing shower. Ionized water from Multi-ionizer also has a sanitizing effect as it kills over 99.9%* of most non-tough, non aquatic harmful bacteria(E. coli , E. coli O157:H7, Salmonella, VRE), which helps to remove rancid odors. *When used as directed. See Directions for Use. *Directions For Use 1. For Sanitizing: Spray fresh ionized water on nonporous hard surfaces for 10 seconds and then wipe the surface completely dry with a clean cloth to kill over 99.9% of most non-tough, non-aquatic harmful bacteria (E. coli , E. coli O157:H7, Salmonella, VRE) . Use only freshest ionized water. . 2. For Cleaning: Use fresh ionized water on nonporous hard surfaces such as stainless steels, glasses, coppers, ceramics, marbles etc as a general purpose cleaner (chemical free). To clean porous soft surfaces such as plastics, clothes, rubber etc, use detergent by up to 20 % of normal usage for best cleaning results. To remove old or oily or stubborn dirt, a bit of detergent can be used with a soft brush and then spray ionized water.

(Quotes from two selling places on the net)

This is quite unclear in how this supposed to work and even though there appears to be an analytical report, prizes and patents awarded, this does actually mean nothing. Nothing good.

How is this supposed to work? There is no energy source, no consumables to replace in this shower head.
The comparison with Yosemite Falls is interesting. A natural waterfall is claimed to provide half the effect of this product? What would be the result of comparing this product with an ordinary shower head? Is the water from the waterfall germicidal?

Well, water is known to dilute bacteria and also removes quite some smells. And this effect is greatly enhanced if you do what you apparently always do when showering: "use detergent by up to 20 % of normal usage for best cleaning results."

This may be a shower head with a good internal design. Without a sound explanation of the functional principles or any proof provided by manufacturer or sellers that all these effects are really there to observe: one of many bogus products on the market. Although ironically it is probably not so harmful to your skin, compared to normal water from other shower heads, since it just will not work as advertised.

  • Thanks for your input. I didn't link to the product in this question because I figured other claims were out of scope and wanted to focus on this single claim. I think most of your answer is more suitable to my question on skeptics.SE (which is currently deleted since it was "poorly written" according to folks there, but I will rewrite it soon). – Skippy le Grand Gourou Jan 12 '18 at 12:23
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    You are right about this and thx for such focus. Mainly meant as an addendum to your answer, since I was searching along those lines you already wrote up. Some water is too contaminated for use but this device is for germaphobes and 'inspired' people – if it would work. – LаngLаngС Jan 12 '18 at 12:33
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Disclaimer : I am not a lawyer biologist, please consider my interpretations with caution.

Note that plain water by itself wash a large amount of bacteria, especially when coupled with rubbing — and a shower usually lasts much longer than 15 s. There may be significant differences between the adhesion of bacteria tested in these studies and bacteria of the skin flora, though. (Or it may imply that antibacterial soaps only have a small effect, hence the mitigate results reported below.)

Anyway, Innate Immune System of Skin and Oral Mucosa (Nava Dayan & Philip W. Wertz, 2011) provides interesting informations on the effects of antibacterial soaps. I don't have access to the full book (and to its bibliography neither) but found the following extracts on google books.

The section

5.3 PROTECTIVE ROLE OF RESIDENT MICROFLORA

Contains a cautious consideration :

This protective role of normal flora suggests that an excessive use of antimicrobial skin cleansers because of not exhibiting a selective mode of action may make the skin vulnerable to infection by more hostile Gram-negative bacteria rather than protecting it [43-45].

The following section is of particular interest (I had only access to pages 96-97, though) :

5.6 EFFECTS OF SKIN-CLEANSING PRODUCTS ON SKIN MICROFLORA AND SKIN IMMUNITY

About skin flora population :

A comparative study on the effects of antibacterial deodorant soap containing triclocarban versus a plain soap on the skin flora found no significant difference in total colony counts [192]. However, more S. epidermidis was observed with plain soap, while washing with deodorant soap resulted in higher colonization of Acinetobacter calcoaceticus and Micrococcus luteus.

A latter sentence about another soap using the same antibacterial seems to contradict the above observation (maybe because of different settings or concentrations ?), though :

Both antibacterial soaps showed significant reductions in the skin flora

About microbiota regeneration :

These observations may indicate that mere washing of skin with plain or antibacterial soap does not disturb or alter the bacterial population in any significant way. Antimicrobials may cause reduction in the density of the skin flora for a short duration, and the skin flora tend to regrow to the previous level within 24-48 h.

About invasion of pathogenic bacteria :

There are also some misconceptions that regular use of antibacterial soap would lead to sterile condition and increase the risk of invasion by pathogenic organisms. […] [As of 2011] no evidence exists that the use of antimicrobial products may alter the ecology of resident skin bacteria that would lead to the overgrowth of pathogenic bacteria [185].

About resistance against antibiotics : [beware, likely outdated information, see DoctorWhom's comments — I'll edit with more details when I find some time to dig this topic]

Does the regular use of antibacterial soap by general population could lead [sic] to the emergence of resistant pathogens ? This issue has been widely debated in the scientific community [166-169]. [As of 2011] there has been no evidence of the development of cross-resistance to antibiotics due to the use of antibacterial wash products in the community [170-171].

Last but not least, I guess details are on a page I don't have access to but the authors state that

the use of antimicrobials may induce irritant and allergic contact dermatitis in some users

Finally, I guess this quote is a good summary of the state-of-art on the topic as of 2011 :

Clearly, more work would be needed to clearly understand the effect of long-term usage of antimicrobial-containing skin cleansers on skin microbiota.

However, the question is not about antibacterial soaps, but about antibacterial water. During a shower, soap is generally applied only for a few seconds on the skin before being rinsed. On the other hand, the skin is typically exposed to water during more or less 10 minutes, which is about 60 times longer. Assuming a similar antibacterial power, the effects of antibacterial water would be much larger than those of antibacterial soaps (all other things being equal, e.g. rubbing).

It would therefore probably be safer to avoid showering with such water.

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    The 'resistance' part is probably not so much applicable here. From a theoretical view the main problem is the assumed wholesale destruction or removal of everything, including beneficial bacteria. But I think the analogy you used holds up. – LаngLаngС Jan 12 '18 at 12:38
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    You're right, I've reordered arguments so that it doesn't appear as the first one. – Skippy le Grand Gourou Jan 12 '18 at 12:54
  • Note that as far as the device I was interested in is concerned, it should be about as safe as plain water... – Skippy le Grand Gourou Jan 12 '18 at 18:29
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    Very important item needing edit: "there has been no evidence of the development of cross-resistance to antibiotics due to the use of antibacterial wash products in the community" is not true, they've actually banned triclosan soaps in the USA for this reason. See fda.gov/ForConsumers/ConsumerUpdates/ucm378393.htm with pertinent quote " laboratory studies have raised the possibility that triclosan contributes to making bacteria resistant to antibiotics. Some data shows this resistance may have a significant impact on the effectiveness of medical treatments, such as antibiotics." – DoctorWhom Jan 15 '18 at 20:14
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    I realize you're likely not talking about triclosan being the additive of the shower water, but for accuracy sake it's important to note there are harms to antibacterial treatments. There is terrifying resistance emerging. – DoctorWhom Jan 15 '18 at 20:17

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