Maybe you live in the most temperate spot in the country, but the rest of us live in places that experience extreme temperatures one way or another. Some places get very hot, some very cold, and a large chunk of the United States goes through both on a yearly basis.

But even when it’s uncomfortable or even dangerous to be outside, life goes on, and we still have to transport ourselves to work, school, the store, the mechanic, and a bunch of other places our feet alone can’t take us.

So, in our efforts to be prepared for when the elements turn against us (along with our human desire for having everything we could ever need at an arm’s reach), many of us are guilty of stockpiling a huge variety of stuff in our cars for whenever we might need it.

The great irony in all of this is the things we might need the most during extreme temperatures don’t hold up very well in those temperatures. This problem gets worse when we leave these things in our cars, which can turn into ovens or ice caverns when we’re not using them.

Here are things that might seem tempting to keep in your vehicle for safekeeping, but you really shouldn’t.

Things Sensitive to Heat

The Counterintuitive One

Want to hear something ridiculous? Sunscreen loses its chemical composure under extreme heat. That sounds like a design flaw, right?

When the weather is hot and it seems the most logical to wear sunblock, it can’t work at peak efficiency. But it’s the truth! Sunscreen loses its effectiveness when subjected to high temperatures. Even beyond this, have you ever put hot sunscreen on your skin? At best it feels kind of gross, but at worst it feels like you’re slathering yourself in lava.

Don’t Waste Your Food

At least it makes sense when things like groceries and food spoil under hot conditions. Anything even remotely perishable will go bad if it’s not refrigerated, of course, but even non-perishable foods can get weird if you really push it (maybe don’t leave chocolate in the glove compartment). The same goes for pet food.

Then there’s wine, which in a best-case scenario, can lose its color when it gets too hot. In worse instances, not only will the flavor be affected, but the heat can make the contents expand, squeeze the cork out, and spoil the wine from exposure.

Oh, and just recently, some researchers have begun tossing around the hypothesis that overheated wine can synthesize into carcinogenic compounds. So much for a glass of wine being good for you.

Messy, Messy, Messy…

Then there are things that are liable to melt in extreme temperatures, like lipstick, crayons and paintings.

Then there are other things that are liable to explode, like lighters and batteries. While it’s always a good idea to keep a flashlight in your car for emergencies, the batteries that power them might mean you have to gamble on not needing it when it’s expected to be obscenely hot out.

But something even scarier than a small explosion might be germs. If you’re coming back from the pool or the beach on a summer’s day, don’t let your soggy swimwear and wet towels linger in the car too long, or the heat can make it the perfect incubator for bacteria to spread.

Stay Hydrated?

Perhaps the most inconvenient truth is it’s not a good idea to leave plastic water bottles in a hot car. As much as it would be nice to have a supply of water waiting there for you when it’s boiling outside, the fact of the matter is water bottles exposed to prolonged heat will deteriorate, and many plastic water bottles contain chemicals like BPA which can contaminate the water and cause numerous health risks, including cancer.

Keeping hydrated while in your car is still a good idea, however, so the best solution here would be to keep water in a reusable container that isn’t made of plastic and doesn’t contain chemicals harmful to you nor to the environment.

Things Sensitive to Cold

More Troubled Food

While most groceries need to be kept out of extreme heat, many also don’t fare so well in the extreme cold.

Eggs are notoriously bad at handling freezing temperatures, as they tend to crack and spoil. Similarly, canned foods can freeze and expand in their containers thanks to their water content, thereby piercing their containers and ruining themselves.

Both frozen eggs and canned goods can theoretically be salvaged, but if and only if they’re undamaged and allowed to carefully thaw in a refrigerator (and even then, the FDA insists you just toss them out if you have any doubts about their safety).

Perishable Non-Foods

Other substances react poorly to cold temperatures. Liquid cleaners like detergent and dish soap can also freeze and burst due to their water content, and paint can coagulate and make it impossible to evenly spread on a wall.

Certain metals and wood pieces can shrink and warp and crack, so on the off chance you have any musical instruments in your car, especially brasses or woodwinds, it might be best to get them out.

I Swear They Just Want Attention at This Point…

You know what else shouldn’t be left in a freezing car? Water bottles. Yes, again. They can implode in the heat and explode in the cold. Actually, there are many things that don’t fare well at either end of the thermometer…

Annoying Things Sensitive to Both


Extreme temperatures really mess with atmospheric pressure, so pressurized things like soda cans and aerosol cans both can pop if they’re forgotten about in your trunk during the summer or winter.


Plants can wither to death in extreme heat or they can shrivel up and die in extreme cold. Depending on your values, this can range from a minor annoyance to an outright tragedy.


Many electronics make clear to keep them stored in a cool, dry place specifically because their components can’t handle very hot or cold environments for very long. So now you have more than one reason not to leave your phone on the passenger’s seat.


Then there are things that can be a little more dangerous if left neglected in your car. Eyeglasses don’t fare well in the cold and their metal frames can actually shatter if it’s severe enough.

But they’re even worse in the heat, where the temperature can warp the metal and frames (and in the case of sunglasses, their filtering layer can start peeling off). or If you left the glasses in direct sunlight, the metal could even scald you.


Medicine left in a car might not hurt you so much as it will stop helping you. Many medications lose their effectiveness when subjected to extreme temperatures, and if you rely upon these, this can put you in danger.

According to experts, things like insulin and anti-seizure prescriptions are particularly bad at losing their potency when they get very hot or cold. Like electronics, these are often recommended to be stored in cool, dry places for a good reason.

Even if the medicine you keep in your car isn’t imperative to your health, it can still be a massive nuisance when they go bad. You don’t want to get to your car desperately wanting to get rid of a headache, only to find that the liquid-gels you’ve kept in your center console for months melted in the summer and fused together in the winter; that will probably only make your headache worse.

Living Beings

Maybe this last one should be the most obvious, but every year people leave children, elders, handicapped people and pets in sweltering or freezing cars, and this often ends as badly as you might imagine.

Perhaps we think deep down parked cars are safe places since they only exist to keep us safe while moving us, so when they’re not moving, they must be even safer, right? But even if this is a flaw in fundamental human logic, you don’t want to be the one to makes this mistake.

So, What Should We Keep in Our Cars Year-Round?

Honestly, the best idea might be to keep it strictly to what is necessary: gas in the tank, registration in the glove compartment, and some emergency supplies in the trunk. Even those might not be completely safe, so anything you keep in your car is subject to risk on some level.

But when it comes time to make a tough decision about what you should and should not carry with you, now you know what’s really not a good idea. You can start by getting rid of that “emergency” 24-pack of water bottles in the trunk that you don’t remember buying and which now feel like Play-Doh.