How Do Hand Sanitizers Work?

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Alcohol-based hand sanitizers are the ubiquitous little squeeze-bottle heroes of airports and hospitals, our allies against the flu and supposedly effective against all the things that ail ya. But what’s in there? And is it true that they kill 99.99% of germs, as popular brands claim? Most popular hand sanitizers are alcohol-based.

The active ingredient is around 70% alcohol, depending on the formulation. The alcohol can be either ethanol, which is the same stuff that’s in your booze of choice; isopropanol, the stuff in rubbing alcohol; or n-propanol, rubbing alcohol’s chemical sibling.

They all pretty much work the same way, which is by dissolving the outer coats of bacteria and viruses and basically exploding them. Alcohol is polar, with water-loving hydroxyl groups. And it loves to disrupt the protein and lipid molecules that make up both bacterial membranes and viral envelopes.

When those all-important outer coats fall apart, these disease-causing culprits literally spill their guts all over the place, leaving them in no position to make anyone sick. But what about people who never touch hand sanitizer because it will breed unkillable super-germs that will kill us all? That’s a valid concern with antibiotics, which are chemicals that target some specific point in a bacterium’s life cycle.

The antibiotics in antimicrobial hand soap can lead to the emergence of bacterial strains that are resistant and harder to kill. But resistance isn’t really a problem with alcohol-based hand sanitizers.

Bacteria can’t develop resistance to having their proteins and membranes blasted. So these alcohol-based hand rubs aren’t going to stop working. Make sure they are alcohol-based, though — some contain antibiotics instead of alcohol, and those do carry the risk of resistance. But alcohol and water alone do not make goo. It’s alcohol that does the germ-murdering, but there’s other stuff in there too.

The biggest one is glycerol. Glycerol is chemically an alcohol, but unlike its cousins, it’s in there not to kill germs but to give the hand sanitizer its gooey consistency that makes it more portable and easier to use. Otherwise it’d be like pouring vodka on your hands. Don’t pour vodka on your hands, guys. Alcohol, water, and glycerol are all you really need to make a DIY hand sanitizer.

Throw in some hydrogen peroxide to inactivate bacterial spores, and you’ve got a recipe that gets the U.N.’s seal of approval.

How Do Hand Sanitizers Work?

But while alcohol is all you need to kill germs, it’s not all that goes in there. Ethanol and isopropanol can dry your skin.

Glycerol helps counteract that effect, but so do a host of other additives manufacturers might put in. This often includes tocopherol [to-cough-fer-all] acetate, a molecule very similar to vitamin E that also happens to be great for your skin, – and familiar stuff like aloe. A host of colors and fragrances might also go in there. None of those are necessary for the hand sanitizer to work, but they might make your hands smell nice. Ahhh!

Toasted Marshmallow! Ethanol-based hand sanitizer might also contain bitter or bad-tasting compounds to stop the small percentage of desperate people out there who are willing to drink it because, well, it’s alcohol.

So do these chemical goo recipes really kill 99.99% of germs? Those numbers are usually the results of lab testing.

But real life is messier. And the effectiveness of hand sanitizer varies based on how oily or dirty your hands are, how much alcohol is in there, and which germs you’re actually talking about. Under ideal conditions, some disease-causing germs really do get zapped at that rate, but others don’t. OH and one more thing. Hand sanitizers work best in combination with hand washing, because they don’t physically remove dirt and gunk from your hands.

So don’t forget that soap and water. Are you always packing hand sanitizer, or an alcohol goo-phobe? Sound off in the comments, and tell us what other everyday chemistry we should cover! Be sure to subscribe on your way out, and we’ll see you next time..

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