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There has been a lot of insistence in some quarters that hand sanitizers need to have > 60% alcohol contents, even against the new coronavirus and so that e.g. vodka (which typically has lower concentration) would not be effective, e.g.

Almost as soon as the news broke about COVID-19 (the official name for the illness caused by the virus), conspiracy theories, hoaxes, and misinformation spread like wildfire online — even from some traditionally reputable information sources. [...] Here are seven myths or hoaxes that we found, and what the reality is.

MYTH: If you can’t get hand sanitizer, you can make your own with vodka.

REALITY: Thanks to several social media posts, including one originally linked to Good Housekeeping, Tito’s Handmade Vodka has spent two days on Twitter telling people, individually, not to use their vodka to make hand sanitizer.

“Per the CDC, hand sanitizer needs to contain at least 60 percent alcohol. Tito’s Handmade Vodka is 40 percent alcohol, and therefore does not meet the current recommendation of the CDC,” Tito’s tweets say.

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    FWIW, you also have to be careful with hand sanitizer, as it dries out the skin, which causes micro-lesions, which in turn makes it easier for infections to enter the body. Also, COVID-19 has a lipid membrane, which is easily broken down with soap without the need for alcohol, so the recommendation for the general public is to wash their hands with soap instead of hand sanitizer, and to leave the sanitizer for the hospitals, where MRSA is more of a problem than in the outside world. – Simon Richter May 17 '20 at 10:33
  • @SimonRichter It is often impossible to properly and often enough wash your hands during commuting and other travel (shopping and so on). Or before eating street food. The hand sanitizers are in this case useful also for the general public. Here they presently required to be available in the shops. Also useful after touching suspisous surfaces in pubic areas because even though later touching one's face is strongly discouraged, it is very hard to be avoided. – Vladimir F Героям слава May 17 '20 at 12:43
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    Slightly off topic: it is for sure an *expensive* hand sanitizer (due to tax on alcoholic beverages) – cbeleites unhappy with SX May 17 '20 at 13:35
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    @SimonRichter: soap is actually a more complicated business. For many germs it's mainly the effect of washing them away that matters. For enveloped viruses there is indeed some (surprisingly rather recent) research that soap acts as a disinfectant, i.e. inactivates enveloped viruses even without "washing away". However not all soap compounds were equally good at this, so the soap formulation might matter: https://medicalsciences.stackexchange.com/questions/23664/how-quickly-does-soap-inactivate-enveloped-viruses-e-g-influenza-compared-to – Fizz May 17 '20 at 15:23
  • @SimonRichter: It's alas hard to find a direct comparison between soap acting merely as an antiseptic and received antiseptics. The (soap-company sponsored) study I found (linked previously) used a 3-min window, which is a fair bit longer than usually used for hand sanitizers. – Fizz May 17 '20 at 15:25
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    @cbeleitesunhappywithSX vodka and 70% hand sanitiser are around the same price for me right now (at least in consumer-sized quantities) due to shortages of the latter – Tim May 17 '20 at 22:47
  • @VladimirF ('s comment, at everyone; especially my fellow Americans) - what are you doing in public places touching suspicious surfaces? It wouldn't be hard to avoid if you we're *not* avoiding the one thing you're supposed to be doing which is staying home, where I'm sure you own soap, can cook at home what you buy every two weeks, and **leave the sanitizer for the hospitals**. – Mazura May 18 '20 at 11:29
  • @Mazura that might be the position of the US government. That is not the whole world. The lockdown has ended in many European countrias. People are **NOT** supposed to stay at home, they are supposed to work. That includes commuting. There are many surfaces that many people touch there. The **availability of sanitizers** at shops **is mandated** by the government and the **hospitals have enough** of the danitizers they need. Alas, even theatres and galleries are opening now. People are not supposed to just shop every two weeks. – Vladimir F Героям слава May 18 '20 at 11:44
  • @Tim: at a quick glance, vodka of around 38-40 % EtOH starts at ≈15 €/l. Both Isopropanol >99% and denatured Ethanol 95% (including packages that explicitly say the denaturing is compatible with use as hand disinfectant) are available for < 10 € for 1 l (and 6-8 €/l if you go for >5 l). In other words, you can prepare hand disinfectant from that for about half the price of vodka and at the same time don't need to worry about the disinfecting properties. You can also buy 70 %v/v isopropanol at somewhat higher prices around 12 €/l, so still below the vodka. We may have a different idea of what.. – cbeleites unhappy with SX May 18 '20 at 14:25
  • @VladimirF - It would be a pretty privileged attitude in the US as well. Most US citizens live paycheck-to-paycheck, and would soon get thrown out of their "home" if they did nothing but stay there. Then add in all the folks who have necessary infrastructure jobs (healthcare workers, food supply chain workers, police, fire, auto repair, etc.). Simply, very few are in a privileged position where they can stay home 100%. – T.E.D. May 18 '20 at 14:28
  • ... is consumer sized. If you go down to 100 ml or so, you'll obviously have to pay for the re-packaging - and while small schnaps bottles down to 50 ml are sufficiently common that the distilleries have bottling lines for that, plain isopropanol in 100 ml bottles is a niche product, whereas 1l, 5l ... up to whole train waggons are more usual. – cbeleites unhappy with SX May 18 '20 at 14:29
  • @Tim: maybe more to the point: if for the same price you get a product you know to be fit for purpose and one of which you do not know whether it is fit for purpose, why go for the questionable one? There may be a difference in local availability of suitable ethanol, though, since here in Germany local distilleries at the moment have an emergency license to produce ethanol for (hand) disinfectants: this usually requires a special license since pharmaceutical regulation comes into play. – cbeleites unhappy with SX May 18 '20 at 14:43
  • I was in Poland when the outbreak starting. Unsurprisingly, it is totally normal to be able to find 90 degrees alcohol you can mix for your drinks in many of the supermarkets, right next to Vodka, etc – Thomas May 18 '20 at 15:59
  • @Thomas I picked up a bottle of "Spirytus Rektyfikowany" (Rectified Spirit) which comes in at 96% when this all started. As I understand you actually need to dilute it make it effective. – JimmyJames May 18 '20 at 21:35
  • @cbeleitesunhappywithSX taxes on alcohol (and therefore the cost of vodka) depend heavily on the country. In some places it can be quite cheap. – fqq May 18 '20 at 22:59
  • Here in Russia a 100ml of sanitizer costs more than 900ml of vodka, so the question is very practical. DIY vodka is 4 times cheaper than that. – Barafu Albino May 19 '20 at 10:07
  • If you are somewhere that you have vodka on hand, you almost certainly also have access to soap and water, which is more effective than hand sanitizer, and places where you would need to use hand sanitizer (when doing errands in the car for example) there are generally laws against having open containers of vodka, so I'm not sure who would benefit from this solution – Kevin May 19 '20 at 17:14
  • As was said, vodka by itself is not a (good enough in this case) hand sanitizer. But it can be used to make hand sanitizer, just like any other alcoholic beverage, with sufficient(ly good) distillation. So, while what you stated in "REALITY" is 100% true, it's not actually related to what you stated in "MYTH". You might rather refer to the myth that vodka is in itself a good enough hand sanitizer (which you state is false), instead of its viability as an ingredient for making hand sanitizer. – Blueriver May 19 '20 at 23:10
  • You know, 85% ethanol is available cheap, by the gallon, at many gas stations. – Harper - Reinstate Monica May 20 '20 at 02:39

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A more recent study (also published by the CDC) seems to indicate that 30% might be a good enough concentration against SARS-CoV-2:

enter image description here

[Figure legend:] Effect of commercially available alcohols in inactivating SARS-CoV-2. The means of 3 independent experiments with SDs (error bars) are shown. A) Results for ethanol. B) Results for 2-propanol. Dark gray bar indicates cytotoxic effects, calculated analogous to virus infectivity. Dashed line represents limit of detection. Reduction factors are included above the bar. The biocide concentrations ranged from 0–80% with an exposure time of 30 s. Viral titers are displayed as TCID50/mL values. LLOQ, lower limit of quantification; SARS-CoV-2, severe acute respiratory syndrome coronavirus 2; TCID50/mL, 50% tissue culture infectious dose.

[...] Conclusions: [...] ethanol and 2-propanol were efficient in inactivating the virus in 30 s at a concentration of >30% (vol/vol). Alcohol constitutes the basis for many hand rubs routinely used in healthcare settings. One caveat of this study is the defined inactivation time of exactly 30 s, which is the time recommended but not routinely performed in practice.

Having said this, antiseptics and disinfectants (in general) are binned in roughly 3 categories based on what they can deal with. Mycobacteria (e.g. tuberculosis) and bacterial spores are a harder (and respectively a lot harder) to inactivate/kill than viruses. (Some antiseptics were even contaminated with mycobacteria.) So (besides possible non-compliance with the recommended use/rubbing time) this is a good reason to demand greater alcohol concentration in general-purpose alcohol-based antiseptics.

Furthermore, even just a far as alcohol effectiveness against viruses is concerned, a 2019 Japanese study of influenza A virus (IAV) inactivation by ethanol found that [non-dry] mucus constituted an extra protective layer for the virus (besides its own envelope), slowing the effect of ethanol-based disinfectants (EBDs) about eight times:

Our clinical study showed that EBD effectiveness against IAV in mucus was extremely reduced compared to IAV in saline. IAV in mucus remained active despite 120 s of AHR [antiseptic hand rubbing]; however, IAV in saline was completely inactivated within 30 s. Due to the low rate of diffusion/convection because of the physical properties of mucus as a hydrogel, the time required for the ethanol concentration to reach an IAV inactivation level and thus for EBDs to completely inactivate IAV was approximately eight times longer in mucus than in saline. On the other hand, AHR inactivated IAV in mucus within 30 s when the mucus dried completely because the hydrogel characteristics were lost.

(30s is the hand-rubbing typically recommended for antiseptics when used as hand sanitizers.)

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    I would phrase your first sentence more carefully. For example "One recent study showed that technically 30% solutions are effective, but expert advice so far has generally been to use higher concentration solutions." – Nobody May 17 '20 at 12:41
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    There is a difference between lab and real conditions: As you rub your hands, the alcohol quickly evaporates and reduces the volume fraction of the solution on your hands, especially if you use a small amount. Given how sharp the drop is between 20 and 30%, it looks meaningful to recommend a higher percentage. In fact, the first article does not recommend any precise alcohol content. – Tony May 19 '20 at 06:15
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    Wouldn't the differentiation between an antiseptic solution, and a beverage play into it? Sure, the vodka may be 40% or whatever by volume, but it may have other properties that would impede it's effect when trying to disinfect a surface? – Larian LeQuella May 19 '20 at 18:39
  • @Nobody Do you mean phrase it more carefully or phrase it to agree with your idea of what's right and relevant right now? I'm not saying you shouldn't use real hand sanitizer, 60%+ alcohol, if and when you can. But that wasn't the question, and the second part of your suggested sentence is conjecture until cited properly. While I fundamentally agree with you, not the point of this Q&A. To try and state it simply, the fact there are more effective options doesn't mean this isn't effective, which is the question. – TCooper May 19 '20 at 22:43
  • @TCooper It's the duty of answerers to properly cite their answers, a comment is just a comment. And yes, I mean phrase it to make it right, because now it's wrong, if you want to word it that strongly. If you go check a study hand rubbing solutions, or more specifically one on alcohol evaporation in hand rubbing, then it will quickly become obvious that 30% isn't going to work unless you dip your hand in a bucket of it. A distinction which this answer doesn't make clear. Edit: And the answer does actually cite a second study relativizing the claim the answer makes boldly in the first sentence – Nobody May 20 '20 at 07:14