10 things not to leave in the car on a hot day

We all know that inside cars it gets hot when the sun shines. But did you know that if the outside temperature is 16°C, a car’s interior can get to 38°C (100°F)? Or that if it’s 22°C outside, inside it will reach 47°C? Opening a window won’t do much good. According to dog welfare charity the Dogs Trust, it’s a myth that dropping the windows a few centimetres will keep a car’s interior cool.

Written by James Foxall
Written by James Foxall
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The greenhouse effect is behind this extreme heating. This is where sun shines onto areas such as the dashboard or seats. The heat is absorbed and then radiates back out. But because a car is closed the heat can’t go anywhere. And that’s why it can be dangerous to leave items inside cars on hot days. Here are 10 things to avoid – some more surprising than others.



Less than 20 minutes in a hot car could prove fatal to a dog. Should its body temperature exceed 41 degrees C, vital functions can start to fail and it could die. Yet research by the Dogs Trust showed that more than one in 10 people know of a dog that’s come to harm in a parked car during hot weather.



Although it doesn’t warn of this on sunscreen bottles, they have been known to explode in hot cars. That means the interior will be covered in the stuff. And if you’ve ever spilt a drop on the carpet you’ll know how difficult it can be to remove. Even if that doesn’t happen, extreme heat can cause the ingredients within the liquid to break down and separate.


Cigarette Lighters

Many cigarette lighters come with a warning that they shouldn’t be exposed to prolonged sunlight. This is because by their very nature they are highly flammable. And if a cigarette lighter explodes there are plenty of small pieces of metal to be fired around the cabin like shrapnel, potentially damaging glass or fragile touch screens.


Electronic equipment

Anything with a battery, whether that’s a digital camera, a smartphone, portable sat nav, tablet PC or MP3 player, will suffer in the extreme heat. The battery and internals generate heat in normal operation. Cooling is sufficient for regular temperatures but hot weather can cause damage to delicate internals such as memory cards, circuit boards, lenses and batteries.



You only have to leave a plastic bottle in the sun for a few minutes to notice how it becomes soft. But with water bottles, there’s a further concern. Plastic contains chemicals such as Bisphenol A and phthalates which bind the various ingredients together. Heat can cause these to be released into the water. And you probably don’t want to drink a liquid laced with extra ingredients that have difficult names to pronounce.


Metal canisters

It doesn’t matter whether it’s sunscreen, hairspray, or deodorant in your gym bag, aerosols don’t like extreme heat. Once temperatures reach around 48 degrees C, experts say the pressure inside a canister increases sufficiently to cause an explosion.



The Royal Society for the Prevention of Accidents can’t recall a single case in the UK where a child has died after being left in a hot car. That’s not to say it doesn’t happen, or that it’s safe to leave children in cars. American Reggie McKinnon made headlines after forgetting his 17-month old daughter Payton was asleep in the back of his car. When he returned after three hours she had died inside the stifling cabin of his SUV.



You spend a lot of money on lipstick and then go and leave it in a hot car. It doesn’t take much for lipstick to go soft at the best of times and it’ll easily melt in a sweltering car.



Soft drink or things that are a little stronger suffer in the heat. As with other metal canisters, the contents of drinks tins or bottles expand with the heat so when you open them they could go anywhere. That’s if the extreme heat doesn’t cause them to burst first. And experts claim the way wine ages and tastes can be altered if it’s left in a hot environment for too long.



You only have to think back to school chemistry lessons to remember that heat alters the structure of things. And that includes the active ingredients of the medication. Look carefully on containers and you’ll see some prescription medication must be stored in the fridge while other more common treatments such as Piriton and Nurofen shouldn’t be exposed to temperatures higher than 25 degrees C.

Written by James Foxall
James Foxall

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