What Not To Leave In Your Car During Hot Weather

Tech and battery-related hazards

Electronics and devices

If you work in an office job, you might be asking, “Can you leave a laptop in a hot car?” when heading to drinks after work, but unfortunately the answer is no. Leaving a laptop in a hot car is not a good idea and can lead to serious damage. 

Phones, laptops, tablets, sat navs, and cameras are sensitive to both hot and cold temperatures. In hot temperatures, their internal batteries can swell and leak, screens can crack from thermal expansion, and circuit boards can malfunction. And if you’re in the habit of leaving them powered on, this makes overheating even more likely.

To avoid damage, always opt to take your devices with you, or store them in a shaded, insulated area if removal isn’t an option, out of sight from passers-by.

Vapes and e-cigarettes

Vapes contain lithium-ion batteries, which are particularly volatile when exposed to hot temperatures. These batteries can expand and rupture if exposed to high temperatures, and in rare cases, they can even explode, especially if left in direct sunlight, such as on your dashboard or in a cup holder. Not only that, but the e-liquid can also degrade and leak when overheated.

To stay safe, treat your vape like you would your phone or battery pack and don’t leave it behind.

Batteries and power banks

Loose batteries and power banks are often stored in glove compartments or the centre console, but these areas can become dangerously hot, especially in a heatwave. High temperatures can cause battery fluid to evaporate or create internal pressure, leading to swelling or bursting. And if you repeatedly expose them to these temperatures, you’re also significantly shortening the battery lifespan of your devices.

If you carry an emergency power bank or spare batteries with you, you should store them in a shaded, insulated container and remove them during warmer months when not in use.

Pressurised and explosive risks

Aerosol cans

You might be wondering, “Is deodorant flammable?”, especially with it being such a summer essential to keep handy. Unfortunately, the answer is yes. 

Products that come in aerosol cans, like hairspray and deodorant, are all pressurised and expand rapidly in heat. What temperature do aerosol cans explode at, you ask? At over 50°C, which is easily reached inside a car in summer, potentially causing them to rupture, leading to explosions and even fires.

Always check the manufacturer’s guidelines, and if you do need to leave them in the car, make sure they’re stored out of direct sunlight, though it’s best to avoid it altogether where possible.

Fizzy drink cans

Cans of fizzy drinks, including energy drinks, can explode if the liquid inside expands due to heat. Aside from the sticky mess that can be difficult to clean from your car’s interior, it can also damage upholstery. If the explosion distracts you while driving and causes a crash, you could face a fine of up to £5,000 for careless driving under Section 3 of the Road Traffic Act 1988. 

To avoid this, don’t store drinks in your car for long periods during the summer. Use a cooler bag if you need to bring them on your journey, and take them with you when you leave the car.

Food and drink safety

Perishable items

Foods like baby formula, milk-based drinks, yoghurt, fresh fruit, and even your packed lunch can quickly become a breeding ground for harmful bacteria such as E. coli, Salmonella, or Listeria when left in a hot car. And it's worth noting that spoiled food doesn’t always smell bad straight away, so you could be risking your health without even realising. 

If you’re doing a food shop or packing food for a longer journey, use an insulated cooler bag and avoid leaving items in the car between stops.

Plastic water bottles

There is growing concern about the effects of heat on plastic bottles, which is understandable given the recent research into microplastics. 

Plastic water bottles in hot car temperatures can leach chemicals like BPA and phthalates into the water, especially if the bottle has been reused. Some people have also reported that bottles left in direct sunlight inside their car have acted like a magnifying lens, causing fires to start.

To be on the safe side, opt for stainless steel or BPA-free bottles, and avoid leaving any kind of bottled drink in a hot car. 

Personal care and health risks

Medication

It is really important to understand what happens if you leave medicine in a hot car, especially if you rely on life-saving medication. 

Prescriptions like insulin, antibiotics, and inhalers often have strict storage guidelines. If they aren't stored at the right temperature, medicine can lose its effectiveness, break down chemically, and even become dangerous. EpiPens, for example, can misfire or fail to deliver a full dose if exposed to heat.

As such, always carry your medications with you, ideally in a small insulated pouch, and never leave them in a parked car.

Cosmetics and toiletries

Makeup and skincare items often contain active ingredients or oils that can separate and degrade in high temperatures. 

One of the most important skincare products to have in summer is sun protection, but does that mean you can leave sunscreen in the car? No. SPF can lose its effectiveness when exposed to high temperatures, leaving you at high risk of burning. Retinol-based skincare can also become unstable, leading to skin irritation or it simply not working. 

If you store an emergency cosmetics bag in your car, you should rotate products regularly and avoid leaving them for long periods of time in the summer.

Perfumes and colognes

Alcohol-based perfumes and colognes are flammable, and while explosions are rare, the pressure inside the bottle can build up and lead to it leaking. Heat can also alter the scent itself, breaking down the chemical compounds and leaving you with a fragrance that smells nothing like it should.

To keep your signature scent safe, it’s best to carry it with you or store it in a cool, shaded place.

Birth control

Most forms of hormonal birth control, like the pill, need to be stored between 20-25°C. Birth control left in hot car temperatures can cause the active ingredients to degrade, making it less effective. That means you might not be getting the full protection you expect, which is especially important if you keep a spare pack in your handbag or glove box for emergencies.

The same goes for condoms in hot car temperatures. Heat can weaken the latex or cause it to dry out, increasing the risk of breakage or failure when used. Always check the packaging for storage guidelines, and keep any form of birth control in a cool, temperature-controlled environment wherever possible.

Baby essentials

Dummies, teething rings, bottles, and sippy cups can all warp or degrade in high temperatures, while softer toys can trap moisture and become a breeding ground for bacteria. Even wipes can dry out quickly when left in a hot car, and no parent wants to be caught without supplies.

If you store baby essentials in your car, try to keep them in a shaded spot and in a sealed container where possible. It’s also worth giving everything a refresh after particularly warm days to make sure it’s still safe and hygienic to use.

Everyday essentials and valuables

Eyewear

Sunglasses and prescription glasses can be expensive to replace, so it's worth taking extra care during summer. Plastic frames can warp, lenses can crack, and specialist coatings like UV or anti-glare can start to peel if left in a hot car.

To protect them, store your glasses in a hard case out of direct sunlight or take them with you when leaving the car.

Important documents and ID

Bank cards, ID cards and other plastic documents can easily warp in the heat, and their chips or magnetic strips may stop working if left in direct sunlight. Paperwork like log books, MOT certificates, and insurance documents can also fade, especially if they’re regularly left in a hot car.

To avoid issues, try to scan and store digital copies where possible, and if you do need to keep documents in the car, make sure they’re tucked away in a shaded, insulated spot, such as the glove box.

How to protect your belongings when it’s hot outside

If you have to leave certain items in your car when it's hot, a few simple precautions can go a long way in preventing damage:

• Check for anything heat-sensitive before locking up
• Park in the shade wherever possible
• Use a reflective windscreen sunshade
• Keep items off the dashboard and seats
• Store essentials in an insulated bag or cooler pouch
• Use shaded compartments like the glovebox or under-seat storage
• Ventilate the car by cracking the windows before you get in

Knowing how to keep your car cool in summer can also go a long way in protecting your belongings from damage.

As UK heatwaves become more common, giving a little extra thought to what you leave in your car will help you avoid unnecessary damage and stay safe on the road.