Another one of those sayings that many keep mentioning is that humans only use 10% of their brain. The claim first appeared after Harvard psychologists tested energy reserve theories with a child protégé in 1890. Only a few decades later, in 1920, the claim started spreading through self-help literature and eventually found itself in the world-famous book 'How to Win Friends and Influence People'.

However, this time, the claim is false. The truth of the matter is that, throughout the day, we use 100% of our brain. Sure, the neurons aren’t all firing up at once, but they are active. That’s because it’s not only thinking that happens up there. The brain coordinates our motor functions and keeps involuntary actions like breathing going.

To do one single task like pouring yourself a cup of coffee takes quite a few brain regions to light up. There's getting the idea, then physically getting the coffee pot, deciding on the cup, and remembering the creamer in the fridge—way more elaborate than it might seem at first glance.

When talking to Scientific American, neurologist Barry Gordon said it’s pretty obvious that we employ the whole brain when living our everyday lives. “Let's put it this way: the brain represents three percent of the body's weight and uses 20 percent of the body's energy.”

Gordon thinks the prevalence of this myth is caused by the fact that we all want to believe we are capable of grand things, things that are only possible if there is some untapped brain power at play. However, unfortunately, there’s no such thing.

Another thing that your mom might have told you when you were young is not to go outside with wet hair, especially when it’s cold. According to many, this is a surefire way to get a cold.

However, that is not the case. That is because it’s not the cold that makes you sick, it’s viruses and bacteria. So, whether you go outside with wet or dry hair, your chances of getting sick are the same and dependent on what kind of germs you come across.

What’s true, though, is that going outside with wet hair when it’s cold can damage your hair. Dampness makes your hair vulnerable and, paired with the cold, it can lead to breakage. So there is a reason to avoid it, just not the one your grandma told you about.

Have you ever been told off by somebody for reading in the dark? Stop doing that or you will worsen your eyesight, they say. But they are, again, wrong. At least for now. Sure, reading in the dark can cause eye strain, but researchers haven’t proved that it has any lasting damage. 

Nearsightedness is way more likely to be inherited and could be worsened by continuously looking at something from a close distance (like a screen), the so-called close work. That being said, no one has looked into the long-term effects of reading in the dark, so we can’t be 100% sure. So, it’s always best to err on the cautious side and ensure you’re reading in a well-lit environment. 

So the next time you hear some sort of medical fact that seems to be based on popularity and not logic, be sure to double-check its validity. And if you’re ever not too certain about how to proceed, check with your doctor—they’re always ready to clarify any confusion.