I've been using hand sanitizer at home since the pandemic and I noticed that most brands use 70%. My cousin insists that the more alcohol, the better it kills the virus, but I don't understand why 70% is more effective. Can someone explain the chemistry behind this?
The 70% concentration is more effective because pure alcohol (or highly concentrated alcohol) kills microorganisms so rapidly on the outer layer that it forms a barrier and can't penetrate to the deeper viral structures. With 70%, the reaction is slower and more controlled, which allows the alcohol to penetrate the virus membrane better and destroy it more completely. The water present in the remaining 30% is crucial for this - it helps the alcohol denature viral proteins more efficiently.
It's like when you burn something with something very hot - the surface burns and forms a crust that protects the inside. With 70%, the process is more gradual and it manages to damage everything. 90% alcohol or pure alcohol kills too quickly and that's it, leaving bacteria or viruses inside intact.
That's why all health organizations recommend 70% - it's not a coincidence, it's based on studies about antimicrobial effectiveness. Your cousin means well but in this case "the more the better" doesn't work. Commercial hand sanitizer usually comes with some additional ingredients that help too, but the 70% concentration is really the sweet spot.
Alcohol needs water to work properly - that's why 70% kills viruses better than 90%. When you use very concentrated alcohol, it dries out the virus's outer layer so fast that it creates a kind of protective shell and doesn't penetrate the internal lipids where the genetic material is. The water in the other 30% of 70% gel makes the alcohol penetrate more slowly and more completely, destroying the entire structure of the virus. The thing is, a lot of people think "the more concentrated, the better" and end up buying those pure 96% alcohols, which honestly don't work as well as a properly formulated gel.
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