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If you're using alcohol for cleaning 70% concentrations are better as they actually kill and lyse pathogens at that concentration, while 99% will just desiccate them, allowing for reactivation when in a moist environment.

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My hands, from working with NF/USP Isopropyl alcohol tend to disagree. It desiccates, defats, and generally kills everything in sight.

Of course alcohol is a powerful solvent at any concentration, but there are definitely studies[1] that demonstrate 70% being a bit more effective at disinfecting.

[1]: https://www.webmd.com/first-aid/ss/rubbing-alcohol-uses

That's always been the rule of thumb that I learned growing up too. My dad kept 90% or stronger concentrations for cleaning electrical contacts and other industrial uses, and 70% for first aid and sanitizing, because that's what each was made for.

Well, today I learned. Thanks.

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