I am trying to determine the best recipe/ingredients for a homemade desinfectant/germ killer. I've been researching these as of now:

  • Isopropanol (or even Ethanol)
  • White vinegar
  • Borax
  • H2O2
  • Specific Essential oils (that are supposed to kill germs)

What I want is something liquid, that you can either spray on your hands or on a toilet seat for example, and kills the most germs possible while being easy to make/mix. It should not be corrosive/toxic etc.

Which of these products can be mixed together? Is there any other products I didn't research? Will mixing any of these cancel the effects of the other?

Thank you!

  • $\begingroup$ This question probably belongs in the DIY or Biology SE. $\endgroup$ – Ben Welborn Aug 9 '16 at 13:48
  • $\begingroup$ I think it may belong at least a little bit here, as I'm looking to mix some "chemicals" to produce the best possible "homemade" sanitizer/desinfectant. And for the DIY, I'm saying "homemade" because I want it to be easy to make, without requiring an actual lab. Maybe "homemade" is not the best term. $\endgroup$ – Frederic Houle Aug 9 '16 at 14:11
  • $\begingroup$ What is the metric for success of this experiment? $\endgroup$ – Lighthart Aug 9 '16 at 21:57
  • $\begingroup$ How would you recommend measuring the success of it? I bought a UV light, but that might not be enough (or maybe not effective at all). $\endgroup$ – Frederic Houle Aug 10 '16 at 0:38
  • $\begingroup$ The goal would be to kill enough bacteria/germ so that the immune system can take care of the rest. I guess. $\endgroup$ – Frederic Houle Aug 10 '16 at 0:40

H2O2 is caustic and reactive, but of the list above, it would be the most complete germicide. H2O2 is an oxidizing agent. H2O2 compares well with bleach (bleach is arguably, the king of disinfectants). However, typically the usage level of H2O2 is higher (3%) than other disinfectants. You cannot mix bleach with H2O2 (H2O2 reacts rapidly with bleach). Also, you cannot mix bleach with acid, although many people will mix vinegar and bleach in tiny amounts to give it an extra kick (which it will)... this is DANGEROUS. H2O2 can generally be mixed with (most) acids- especially organic acids like citric acid or vinegar.

Essential oils (especially phenolics like clove, cinnamon, and/or thyme oil) are the most germicidal e-oils, but e-oils are kind of like gasoline (plastic dissolving-staining etc.). Other, terpenic e-oils (like peppermint, pine, citronella, lemongrass, etc.) are somewhat germicidal. Limonene and pine oil are often used as a germicide, although it is comparitively weak to most essential oils. However, they is not as caustic or toxic as clove (for example)- although they do have some toxicity. Pine oil, thyme oil, peppermint, and limonene are popular choices for germicidal use. I have seen thymol and limonene mixtures before. Peppermint is common for school mop-products (becuase in schools, its common to clean up vomit, and peppermint helps quell nausea). Cinnamon, thyme and peppermint are common in mouthwash. Usage levels for e-oils is usually much less than 1%... they are not as effective (but still helpful) as other disinfectants at such levels, but the lower usage is balanced between the noxious-toxicity of the oil and the efficacy of the germicidal effect. Since antibiotic e-oil products would need to contain a noxious and cost prohibitive amount of e-oil to be effective (as a stand-alone antimicrobial), most antibiotic e-oil products (pine-sol for example) contain ammonia (high pH), and simply list pine as a scent (it would help kill bacteria- but to claim antimicrobial on a bottle, the product must be EPA registered and there are lots of problems with e-oils... again, cost, toxicity, and efficacy to name a few). You can mix e-oils with soap and alcohol. Other chemicals (acids, bases, and oxidizers) can/will break e-oils down, but not very rapidly. And the break down/byproducts would probably still have some degree of antimicrobial activity.

Vinegar is used by many DIY people, but it is not a popular commercial product because it smells kind of bad, it's not very effective, and if it is mixed with bleach (WARNING) it can cause a serious health hazard. Also, 5% acetic acid is not extremely germicidal (it will work to kill bacteria in food after a few days); many spores will survive for hours in acetic acid. Vinegar is most effective against non-spore forming (gram negative) bacteria- which are often the more nasty kinds of bacteria (Salmonella, E. coli, Serratia, Pseudomona, etc.)... but it's less effective against spore forming (gram positive) bacteria (Candida, Bacillus, Streptococcus, Micrococcus, etc.). Again, it is an effective preservative in food... as is 5% ethanol (ie., beer). 50% acetic acid is much more effective and it works faster... as does 50% ethanol. pH is a factor, so vinegar is a bit more effective than ethanol, but in general, a high pH is much more effective than a low pH. So, ammonia or lye solutions are more effective than organic acids.

70% isopropanol and 60% ethanol are a common hand and wound disinfectants. They are fairly antimicrobial and antiviral, but again, spores (and other gram positive bacteria) can survive in dilute alcohols (for a little while).

Borax is not germicidal (I don't care what the popular opinion on the internet is). The insecticidal efficacy of borates is also relatively poor, but since it doesn't leave or break down, it is effective over time (weeks, years, etc.)... persistence is why it is used as an effecitive termiticide for wood-framed houses. And although borax is claimed to be effective for roaches... mixed with bait and such- I have tested it thouroughly and it's not very good. But more at the subject here- I would not consider borates to be antimicrobial... unless you consider pH to be the antimicrobial agent. In which case, ammonia or lye are extremely antimicrobial (they really are). But you can't mix lye and ammonia for cleaning (DANGER). Also, bleach has a relatively high pH (about 11).

Notably, but not mentioned, SOAP is the originial antimicrobial and insecticide. It works great; pound for pound- it works better than vinegar. It's been used for centuries, and it has very low toxicity. But, since it has very low usage levels (generally less than 1% in water) and it is more for removing bacteria- so it is not purely germicidal. Generally speaking, soap more strongly inhibits gram positive, spore forming bacteria (at say 0.1% concentration) and inhibits most gram negative bacteria at around 4% concentration. Also, soap manufacturers don't need to pay hefty tolls for registering all their products as antimicrobial because people buy soap anyway. But adding a strong antibiotic (usually triclosan, which tends to work better on gram negative bacteria) they can easily skate through EPA with an affordable antimicrobial product (affordable especially compared with the cost of the claim which costs MILLIONS of dollars).

To claim "antibiotic" with EPA, a product must kill most bacteria (I think it's something like 99.9%, minimum, within 5 minutes against several standard/representative microbial species). You really can't do that without something like 60% ethanol, or 0.15% bleach (ie., 3.33% of a 5% bleach solution), or 3% H2O2, or 2% clove oil (ooh that stings!) or 0.1% triclosan in soap (which gets diluted 100x to about 0.001% in common use) or some antibiotic molecule in high enough concentrations to kill.

Some antimicrobial combinations are synergistic, some are antagonistic, some are additive, and some are deleterious. Most of the reliable combinations of over-the-counter antibiotic materials have already been tried and the best products (soap, hydrogen peroxide, alcohol, bleach, ammonia, and yes, even fragrance) have stood the test of capitalism and time.

Here is some good reading about this: Guideline for Disinfection and Sterilization in Healthcare Facilities, 2008

  • $\begingroup$ So let's say I make a mix of: - 49% of 3% H2O2 (I suppose the 97% remaining is water?) - 49% of 70% Isopropanol (I suppose the 30% remaining is water?) - 2% any phenolic oil Would that make an effective germ killer/desinfectant (I do not really care about EPA standards at this point in my research)? $\endgroup$ – Frederic Houle Aug 9 '16 at 16:03
  • $\begingroup$ Could some lye also be added to the mix? Isopropanol / H2O2 / Lye / Phenolic oil. $\endgroup$ – Frederic Houle Aug 9 '16 at 16:13
  • $\begingroup$ @FredericHoule no. absolutely not. Lye and H2O2 will react. Lye will also decompose e-oils pretty quickly (by comparison with H2O2). $\endgroup$ – Ben Welborn Aug 9 '16 at 16:17
  • $\begingroup$ @FredericHoule H2O2 will mix with organic acids... $\endgroup$ – Ben Welborn Aug 9 '16 at 16:17
  • $\begingroup$ @Bel Welborn so just half/half H2O2 and Isopropanol, and a few e-oils. That would make it? (Thanks for your answer by the way, very very interesting read. I tried to upvote but not enough reputation to do it) $\endgroup$ – Frederic Houle Aug 9 '16 at 16:33

Why trying to reinvent the wheel? 70% ethanol in water is more than enough considering the examples you gave. You can add some essential oil (mainly for the smell).

Note that, to my knowledge, pure alcohol is not a disinfectant. It needs a fair amount of water.

  • $\begingroup$ The problem is, if I want to commercialise that product, it can't have only ethanol or isopropanol, from a marketing point of view. It needs at least 2-3 ingredients, no matter if they are super effective or only minor enhancement. That's why I'm considering mixing 1-2-3 things together. $\endgroup$ – Frederic Houle Aug 9 '16 at 23:34

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