For obvious reasons, hand sanitizer is all the rage right now, to the extent that stores are experiencing shortages, the factories manufacturing it are kicking into overdrive, and even breweries (otherwise shut down temporarily) have converted their machinery to creating branded hand sanitizers.
That's great and all, but what about that bottle you've had sitting up in the cupboard for a few years? Is it still good to use, or does it expire? Then there's the related question: does hand sanitizer protect you on an ongoing basis, like a glove or a shield? Let's find out.
What's In Hand Sanitizer?
First off, let's talk about what goes into hand sanitizer. Most hand sanitizers are made of three simple ingredients: water, alcohol (usually ethyl alcohol, which is derived from grain), and a gelling agent. The water is there to activate the gelling agent. The gelling agent is what makes hand sanitizer a thick goo instead of thin, watery alcohol. The alcohol, meanwhile, is the star of the show. The alcohol itself is what does the actual sanitizing.
In fact, the ingredients to hand sanitizer are so simple, it's actually possible to make it at home. In this recipe, the gelling agent is aloe vera, and they use isopropyl alcohol rather than grain alcohol because it's likely to be the only alcohol you have available in sufficient quantities.
You may have seen recipes to turn vodka into hand sanitizer, but that isn't going to work. Most vodka is around 40% alcohol, 60% water. To make a hand sanitizer, you want a high concentration of alcohol in the finished product, at least 60% if not 80%. There's simply not enough alcohol in vodka (and most other alcoholic beverages) to make a sanitizer that actually sanitizes.
Other ingredients in hand sanitizer include:
- Soap. Some hand sanitizers include a small amount of soap. Soap helps break down dirt and grime, as well as microorganisms that the alcohol can't. It also helps create a bit of lather or foam when using the hand sanitizer, to help it work.
- Perfume. Various scents (or, in the case of the DIY recipe above, essential oils) give hand sanitizer a scent other than alcohol. Many people are bothered by the sterile alcohol scent of hand sanitizer and prefer something with a bit of a floral scent to it instead.
- Hydrogen Peroxide. Typically some small amount of hydrogen peroxide can be added to hand sanitizers as an additional chemical for sterilization. It can break down and kill microorganisms that alcohol alone doesn't, such as bacterial spores.
Remember, though, that the added ingredients in hand sanitizer need to remain under a certain proportion compared to the alcohol. If the concentration of alcohol drops too low, so does the effectiveness of the sanitizer.
Can Hand Sanitizer Expire?
You may have noticed that some bottles of hand sanitizer have an expiration date on them, though that date is usually far in the future, around three years out. Of course, you have to wonder; is the expiration date there for legal liability reasons and the sanitizer is fine even after it passes, or is it a real expiration date?
Hand sanitizer can "expire", but it's a slightly complicated situation. If you find a sealed bottle of hand sanitizer in the back of a cupboard, that hasn't been opened, but was purchased five years ago? That hand sanitizer is probably just fine.
See, alcohol doesn't really go bad, at least in sealed conditions. Something like wine can go bad, but that's because the actual alcohol is a low concentration and things like alcohol-eating bacteria than thrive in the environment once the wine has been opened and exposed. Even then, a wine bottle that is sealed and stored properly lasts for dozens or hundreds of years, right? That's the whole point of wine!
With hand sanitizer, the primary risk is alcohol concentration dropping. Alcohol very readily evaporates and does so quickly. You can see this in action by taking a drop or two of isopropyl alcohol and dripping it on a counter or other surface and watching it for a few seconds. It will disappear quickly as it evaporates into the atmosphere.
In hand sanitizer, if the bottle is sealed, there's no atmosphere for the alcohol to evaporate into. Sure, a little bit of it may evaporate into the bottle, but it will reach equilibrium quickly. 
In an opened bottle, meanwhile, the atmosphere has a hard time reaching it. The opening in a hand sanitizer bottle is very small, and with a cap on it, very little air can circulate through it. You only really lose to evaporation very slowly, or if the cap is left off, and even then, it can take quite a while for any serious amount of alcohol to evaporate out of the sanitizer. This is why the "best by" date for hand sanitizer is three years out.
It's also worth mentioning that hand sanitizers that have more than 60% alcohol in them will take longer to degrade to a point where they are no longer as effective. If your hand sanitizer has 80% alcohol in it, you can probably use it safely and effectively for half a decade without worrying about replacing it.
The other factor that can affect how long a hand sanitizer remains useful is how it is stored. Hand sanitizer that is stored in a small keychain bottle is often exposed to the elements. Hand sanitizer stored in a bottle on a windowsill can also be exposed to sunlight regularly. This exposure to ultraviolet radiation can be damaging to the compounds in hand sanitizer and can cause them to break down. It can also damage the plastic of the bottle over time, which might mean plastic compounds can contaminate the hand sanitizer. It can even make the plastic brittle and more prone to breaking if you drop the bottle.
In general, hand sanitizer left out will not be good for as long as hand sanitizer stored in a cool, dry, dark place. Still, though, it's not usually something you'll have to worry about.
Should You Discard Old Hand Sanitizer?
So what happens if you look and find that your hand sanitizer is years old, well outside of the three-year expiration date? It's worth mentioning that hand sanitizer is considered to have a three-year shelf life by the FDA, even if it doesn't have a date listed on the bottle.
Well, as mentioned above, if your sanitizer bottle is still sealed after all these years – like you bought it and put it away and never had the need to use it until now – you don't have to worry. That sanitizer is just as good as it was before. If anything, maybe some of the perfume in it won't be as strong as it was when it was bottled, but right now, perfume isn't all that important.
If your hand sanitizer is very old and opened, you have a choice to make. You can discard it and get a new hand sanitizer, or you can keep on using it. Unless it's sealed, if its more than a couple years old, I'd probably toss it.
Nothing bad will happen if you keep using "expired" hand sanitizer. It's not going to metamorphose into acid or anything. The only thing that can happen is the alcohol concentration goes down, which means it's less effective at killing germs on your skin. Hand sanitizer is already less effective than washing your hands with soap and water, so a slightly less effective hand sanitizer is still about on par for what we expect hand sanitizer to be. Just be aware that it won't be quite as effective, take proper precautions like washing your hands whenever you can anyway, and that's good enough.
If you do choose to discard hand sanitizer, make sure you do so safely! Hand sanitizer, being a high alcohol gel, is highly flammable. Make sure you know what you're doing when you discard it or follow your city's local regulations for disposing of flammable liquids.
What About Non-Alcohol Sanitizer?
Non-alcohol hand sanitizers exist for people who are worried about alcohol or flammable materials being readily available around their residence or on their person. They can alleviate many of the problems of alcohol-based hand sanitizers, most notably the alcohol's effect of drying out your skin. It's also generally non-toxic.
Alcohol-free hand sanitizers typically use a chemical called Benzalkonium Chloride as the active ingredient, usually in a very small concentration, because it's a very potent chemical. It's quite safe for topical use.
The chemical Benzalkonium Chloride is very stable and has a very long shelf life. Different sources of information differ on how long it can remain stable, but most agree that it is stable for at least three years. Thus, hand sanitizer that doesn't have alcohol in it is going to be stable and effective at least as long as alcohol-based hand sanitizers.
There may be other kinds of hand sanitizers that don't use either this chemical or alcohol, and they will have their own expiration dates. You'll want to check the bottle, or the manufacturer, or the chemical specifics of the chemical that is actively used in the sanitizer to see what they have to say.
How Long Does Hand Sanitizer Last On Your Skin?
Now let's look at the related question. When you use hand sanitizer, what does it do? Does it just cleanse your skin, or does it leave a barrier to protect you as well?
Unfortunately, hand sanitizer is not prophylactic at all.
When you use hand sanitizer, the application of alcohol, benzalkonium chloride, or whatever other cleanser is in the concoction will spread across your hands while you rub them together, killing and denaturing microorganisms on the surface of your skin. This works exactly as well as you rub it in. If you rub hand sanitizer over your palms for three or four seconds, it's going to barely do anything to kill germs. You need to use enough hand sanitizer, and rub it in thoroughly, akin to the 20-second hand washing procedure making the rounds as well.
With alcohol-based hand sanitizers, the alcohol quickly evaporates from your skin once it is done doing its job. With the non-alcohol hand sanitizers, the concentration of the effective chemical is lower, and it quickly is expended when rubbing it in. Either way, it only works while you're applying it.
The moment you're done applying hand sanitizer, your hands are free to be contaminated again. If you put hand sanitizer on and then grab a doorknob, touch your phone, or handle money, you're getting germs back on your hands immediately. There's no residual chemicals or alcohol left there protecting you.
Hand sanitizer is useful as an in-between step. If you touch something that could be contaminated, you use hand sanitizer before you then touch something you don't want to be contaminated. If you touch something before you use hand sanitizer, you should treat that surface as potentially contaminated until you can clean it with a surface cleaner
As it stands, hand sanitizer does not protect you long-term against anything. You can think of it like washing your hands; it works to remove any germs on your hands already, but it does not prevent you from picking up more germs the moment you're done.
With that in mind, maybe you need to change how you're using hand sanitizer, or maybe you were already using it properly. Either way, it's good information to have. Use the hand sanitizer you have, use it properly, and wash your hands when you can for the best effect.
