Health Grades 7-9

Are you a left-brained person or a right-brained person? Spoiler: You're neither. Each of us uses both sides of our brain for most of what we do. But still, there are a number of brain functions that do show lateralization, where they are localized to one side or another. Why is this?

Why are our bodies so symmetrical, but our guts aren't? How does your body know where it's parts should be?

Most of the time, you won't notice it's there, but over the course of your life your immune system will guard you against hundreds of potentially fatal threats. Related Lesson

Today, glasses help millions of people with poor vision be able to see clearly. But how? Our hosts help unravel the answer by explaining refraction. Related Lesson

Our bodies undergo a series of extraordinary metamorphoses: we grow, experience puberty, and many of us reproduce. Learn how hormones drive these changes. Related Lesson

Katharina Ribbeck reveals the mysteries of this transparent, shape-shifting layer that moistens and lubricates the vulnerable parts of our body

The first time feels easy, but each time you life a weight gets harder until you can’t continue. What’s going on?

Halitosis is a curse that has plagued humanity since ancient times. But what causes it, and why is it so universally terrifying? Related Lesson

Body odor is a surprisingly complex phenomenon, influenced by our genetic makeup, age, diet, and hygiene. So what is this odor, exactly?

In about half of the human population, yeast in our hair causes dandruff. So, why do some people have more dandruff than others? And how can it be treated? Related Lesson

Fortunately, doctors today don’t resort to power tools to cure headaches, but we still have a lot of questions about this ancient ailment.

What exactly is a migraine? And what causes it? Let's find out!

If you’ve never had a nosebleed before, the first one can be terrifying. Why is blood pouring out of your face? Related Lesson

At what age are you smartest? Dig into how your brain development affects your skills at different stages of your life. Related Lesson

What role does water play in our bodies, and how much do we actually need to drink to stay healthy? Related Lesson

Travel into the auditory system to explore the constant ringing sensation of tinnitus, why it happens and how to treat it. Related Lesson

Today, about one-tenth of the world’s population are left-handed? Daniel M. Abrams explains what that tells us about the pressures of evolution

The human voice is capable of incredible variety and range. How exactly does our voice box work, and what causes shifts in speech as we age?

You know that little pink thing nestled in the corner of your eye? It’s actually the remnant of a third eyelid. Why do we have it?

You already know that a trip to the beach can give you a nasty sunburn, but the nitty gritty of sun safety is actually much more complex. Wrinkle-causing UVA rays and burn-inducing UVB's can pose a serious risk to your health (and good looks). So what can you do? Related Lesson

Most of us are no stranger to an occasional case of the hiccups. But what causes these ‘hics’ in the first place? Related Lesson

Flatulence is a daily phenomenon. In fact, most human beings pass gas 10-20 times a day (yes, that includes you). Where does your bodily gas come from? Related Lesson

There are a number of scenarios that can make us sweat–including exercise, eating spicy foods, and nervousness. But how does this substance suddenly materialize, and what exactly is its purpose? John Murnan explores the science behind sweat. Related Lesson

Why do we need a new flu shot every year? Vaccines for diseases like mumps and rubella offer a lifetime of protection with two shots early in life; what’s so special about the flu? Related Lesson

Some people love the feeling of cracking their knuckles, while others cringe at the sound. But what causes that trademark pop?

Teeth. We’ve all got ‘em (most of us, anyway). But how do they grow? Teeth are made from some biological nanotechnology that will blow your mind. They are strong enough to last hundreds of millions of years.