But what's in there?

And is it true that they kill 99.99% of germs?

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; isopropanol, the stuff in rubbing alcohol; or n-propanol, rubbing alcohol's chemical sibling.

They all pretty much work the same way though, 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 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 that goo.

It's alcohol that does the germ-murdering, but there's other stuff in there.

The biggest one is glycerol.

Glycerol is chemically an alcohol, but unlike its cousins, it's in there not to kill the 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, come on.

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 will help counteract that effect, but so do a host of other additives manufacturers might put in.

This often includes tocopheryl acetate, a molecule very similar to vitamin E that also happens to be great for your skin, and some familiar stuff like aloe.

A host of colors and fragrances might also go in there.

None of those are necessary to make the hand sanitizer work, but they might make your hands smell nice.

Mmm, mmm, mmm!

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 is alcohol.

So we are back to the question: 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.

You should keep in mind, hand sanitizers work best in combination with hand washing regiment, because they don't physically remove dirt and gunk from your hands.

So don't forget that soap and water.

Do you always have a bottle of this stuff wherever you go, or you are an alcohol goo-phobe?

Sound off in the comments, and tell us what other everyday chemistry we should cover!

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