Sitting inside a car in just mildly hot weather can be dangerous, and potentially fatal. Here’s why.

In warmer weather, your car basically acts like a greenhouse. But the reason it gets so hot is not as simple as you might think. While sunlight hitting the car warms it up, it’s the infrared waves produced inside that are the real problem.

See, your car’s glass actually blocks longer wavelengths of light, like infrared, from entering. These are the wavelengths that radiate heat. But while they can’t get in, they also can’t get out.

As sunlight hits your car, the surfaces such as your steering wheel and dashboard try to re-radiate that incoming energy. They do so via infrared waves, so as The Weather Network notes, they “get rid of excess energy by radiating it as heat.”

The result is that the temperature inside your car can jump massively, even when the temperature outside is not that hot. Even if it’s just 21°C (70°F) outside, a car in sunlight can easily reach 50°C (122°F). You can suffer heat stroke if your body temperature reaches 40°C (104°F), or even less.

The Journal of Emergency Medical Services says that your car can jump a massive 11°C (20°F) if it’s left in the Sun for just 10 minutes. After 20 minutes, it can rise by 16°C (29°F). After an hour, most cars will reach a peak temperature of between 60-82°C (140-180°F). You will not survive long at these temperatures.

When the body is exposed to too much heat, hyperthermia begins. This is basically where our body is producing more heat than it can get rid of. Heart rate and breathing increase as your blood pressure drops. The latter can turn your skin pale or blue as your heart tries to circulate blood properly. Eventually, this can prove fatal as your organs fail.

Cracking the window open, or running the air conditioning beforehand, is not enough to make conditions bearable. The website heatkills.org notes that after an hour, temperatures can still reach unsafe levels even if the window is open a few inches.

If you want to see some examples of how hot it can get, these two videos show what it’s like to stay inside a car on a hot day.

While this is uncomfortable – and potentially deadly – for adults, this can be even worse for children. The website kidsandcars.org notes that a child’s body can overheat three to five times faster than an adult’s.

About 37 children die every year in the US after being trapped in hot cars. More than half of people (54 percent) did not realize their child was trapped in the car. A shocking 87 percent of children who died from vehicular heat stroke were aged three or younger.

And don’t think it’s just the summer months – over the last 16 years, hot car deaths have been recorded every month except January. Just because the months seem cooler, your car is still a dangerous place to be left unattended.

There are a number or simple but effective solutions. Always look before you lock your car. Keep your vehicle locked at home at all times so your child can’t get in it by accident. And if you see a child alone in a car in public, call emergency services immediately.

Pets, too, can suffer in cars. Hundreds of dogs and other animals die every year after being left in overheated vehicles. They can be just as susceptible as humans to the extreme heat.

So, especially in these summer months, be extremely careful. Your car can become a heat death trap, even when temperatures don't seem that high.