A while ago we asked members of the BuzzFeed Community to tell us what strange body myths they believed as a child.
Some were quite out there, but others were a little more plausible – so we set about fact checking them. Here's what you should know about seven of those myths.
1. "You'll go blind if you stare at a microwave for too long."
The Truth
Microwaves cook your dinner by using microwave radiation to make water molecules in the food vibrate, heating it.
It's true that microwave radiation can harm humans (it can basically cook you in the same way it does food). It's especially damaging to eyes, because the lenses of your eyes are sensitive to intense heat. Exposure to high levels of microwave radiation can cause cataracts.
But it's exactly for this reason that there are lots of regulations around the design and safety of microwave ovens. In the US, the Food and Drug Administration (FDA) limits the amount of microwave energy that can leak out of the oven over its lifetime to 5 milliwatts per square centimetre – that's about 100,000 times less power than the radiation inside the microwave itself. Several other countries, including the UK, have set the same safety limit, but in practice many newer microwave ovens are far below this limit, making them even safer.
Another bit of relevant science is that the power of microwaves drops off very quickly the further away from the oven you are. According to the FDA: "A measurement made 20 inches from an oven would be approximately one one-hundredth of the value measured at 2 inches."
TL;DR: Unless you're staring into the microwave with your nose pressed up against it 24/7 for a very long time, you're going to be just fine.
2. "You should pee on a jellyfish sting."
The Truth
That's right – peeing on a jellyfish sting is more likely to make things worse.
When you brush past a stinging jellyfish's tentacle you touch sensory hairs that trigger specialist cells called nematocysts to fire tiny little threads at you. Those threads have barbs at the end to pierce and stay put in your skin, and release venom into the wound, ensuring pain and misery.
Urine and vinegar are widely thought to help with the pain, but the NHS says both might actually make the pain worse. They recommend instead using a credit card or razor blade to remove any nematocysts that are stuck to the skin.
3. "Hiccups mean you're growing."
The Truth
Hiccups happen when your diaphragm contracts. Your diaphragm sits under your ribcage and helps control your breathing.
The NHS lists lots of possible causes, including eating too quickly, drinking alcohol or fizzy drinks, and stress, fear, and excitement, although a lot of the time there's no obvious cause – but growing is not on the list.
Hiccups can affect people of any age, including babies and even foetuses in the womb, which may be where this myth came from.
4. "Eating raw cookie dough will give you salmonella."
The Truth
The important question here is whether the cookie dough contained raw egg or not. Eggs can harbour salmonella bacteria, which can cause food poisoning. The number of laboratory-confirmed cases of salmonella in the UK has been declining since 2000 and dipped below 10,000 in 2010.
Most cases of food poisoning clear up by themselves, but in vulnerable people – young children, the elderly, and people with weakened immune systems – it can be fatal.
Once you cook the eggs (including the yolk), the salmonella bacteria is killed and you're fine. If you want to be totally safe, avoid eating eggs that haven't been cooked – including ones in raw cookie dough. Or just make eggless cookies, and eat the dough to your heart's content.
5. "Too much salt will make your blood dry up."
The Truth
Eating too much salt won't make your blood dry up – in fact, it basically has the opposite effect.
Sodium is a key component of table salt, and also plays a key part in regulating your blood flow and pressure. When there's more salt in your body, your kidneys keep more water in your blood to make sure the balance of sodium to water is right. So rather than making your blood dry up, too much salt ensures your kidneys hold on to more water than they would have otherwise.
According to the NHS, a diet high in salt can cause high blood pressure. For the record, you involuntarily lose about half a gram of salt per day, so that's usually all you need to consume to keep your body happy.
6. "Looking at dog poop will give you pink eye."
The Truth
Let's make this clear: Just watching a dog poo is not going to harm you in any way.
But if you got some of that poo on your hand, and then touched your eye? Yup, that's a great way to introduce some stuff into your eye that you really don't want there.
There are parasitic roundworms that can infect dogs and cause a disease called toxocariasis. Most people who get infected never have symptoms, and the parasites die on their own within a few months. But, according to the NHS, in rare cases it can cause blurred or cloudy vision, or a red and painful eye – and if you don't get it checked out right away, there's a risk it can lead to permanent vision loss, aka blindness.
The roundworms are carried by cats and foxes, as well as dogs. They live in the animal's digestive system and produce eggs that are expelled in the animal's poo. The eggs are only infectious after about two to three weeks, but they can survive for longer than that in soil on the ground, for example.
That's the reason young children are most likely to be infected with toxocariasis – they're the ones most likely to be rolling around in dirt at the park and then sticking their fingers in their eyes.
7. "Living higher up makes you shorter."
The Truth
Gravity does change the further away you get from the ground – but it actually decreases, and the change is very small. Gravity starts to decrease the further away from Earth's centre you get. Its strength changes proportional to 1/R2, where R is the distance from the centre of Earth.
It's also slightly more complicated than that (as always) because Earth isn't a perfect sphere, and it varies in density. Earth's rotation also makes gravity slightly weaker at the equator.
At Earth's surface, on average, the strength of gravity is 9.81m/s2. At the top of Mount Everest, it's just 0.28% weaker than that.
At the height of the International Space Station, the strength of gravity is 90% that at the surface of Earth, but the orbit of the space station makes the astronauts weightless. Even at this extreme, astronaut Scott Kelly only grew 5cm after spending an entire year (almost) in space – and he lost the extra height within two days of returning to Earth.