A distinct feature of a typical skeleton is its permanent, pearly smile — with everything else stripped away, teeth look indistinguishable from bone. But human teeth aren’t bone. 

They have a different composition, made from enamel, dentin, and pulp, which allow them to be extra robust. The downside to that is they can’t heal like a broken bone, and we can’t regrow them, meaning once they’re gone, they’re gone. 

So let’s appreciate these 32 individual teeth, as they’re the only ones you’re ever going to get. Each has its own role to play — there are four main types that serve a particular purpose when it comes to chewing and eating, and some are even crucial for human speech. Here’s a closer look at what our different types of teeth are for.

Incisors

The front eight teeth are arguably the most important ones, known as incisors. With four located on the upper (maxillary) jaw and four on the bottom (mandibular) jaw, the primary function of incisors is to cut and tear into food. 

Picture taking a big bite out of an apple. Now imagine trying to eat one without your incisors. It’s pretty much impossible, right? Incisors are shaped like wedges, which make them perfect for biting into food before offloading some of the tearing and grinding to the other teeth. 

Unlike most of our other teeth, incisors also play a huge role in human speech, and are absolutely vital for forming sounds such as “th,” “v,” “f,” “s,” and “z.” Try saying the sentence “thinking of very fun zebras” without your front teeth touching your tongue or lips. Yeah, not easy.

Canines

The four canines, also known as cuspids (“cusp” refers to the peak-like biting surface), are the most visually distinct of all human teeth. There’s just one in each section of your mouth — top left, top right, bottom left, and bottom right. As their name suggests, these teeth have a sharp, fang-like appearance similar to that of wolves and dogs (and vampires, though bats aren’t canines). The shape makes them perfect for gripping and tearing into tough food, including meat. 

However, compared to the teeth of other carnivores, human canines aren’t particularly adept at the job, and scientists actually theorize that they’re partly an evolutionary leftover from our past. Like other primates, we may have originally employed our teeth for displays of dominance or even as handy weapons in a pinch. But over millions of years, humans (and other species of hominins) evolved smaller teeth, including canines, as we increasingly used tools to cut and tear our food for us.

Molars

Molars’ primary role is providing a grinding surface for food to be mashed into tiny bits before swallowing. These teeth are farthest back in your mouth, so you can see why you wouldn’t use them to tear food but instead crush and grind it.

Most adults swallow food measuring roughly 2-4 millimeters on average, so those molars need to get to work ensuring food bits can safely pass through your throat without getting stuck. To handle the hard work of all that biting pressure, molars have more roots than your front teeth, which help anchor them firmly in the jawbone.

Molars are the largest group of teeth in number — most adults have 12, so they make up more than a third of all your teeth. However, four of them — known as wisdom teeth — are often surgically removed, leaving adults with just 28 teeth total. 

The reason for this peculiar rite-of-passage dentistry is that our biology hasn’t caught up with our evolved diet, making wisdom teeth vestigial structures (no longer necessary) similar to your appendix or tailbone. As modern humans eat more soft, cooked food, the size of our mouths has decreased and we simply don’t need so many teeth anymore. 

Wisdom teeth are the third set of molars and the last to grow, so when they do finally arrive, they often find that there’s no room — not much different than trying to squeeze onto a packed train during rush hour. To avoid overcrowding, around 85% of adults have their wisdom teeth removed at some point.

Premolars, aka Bicuspids

A pair of premolars sits between each set of canines and molars, for a total of eight. With their transitional position in the mouth, premolars move food from the biting and tearing teeth toward mashing and grinding ones, as if what you’re eating is moving down an assembly line toward the back of your throat and into your stomach.

Another name for these teeth is bicuspids, meaning “two peaks,” but premolars could just as easily be called post-canines because they possess features of both types. They’re flat like molars but feature two sharp points that continue the tearing work of the canines.

Baby Teeth

The adult mouth contains four primary teeth groups, but we can’t forget our first set of chompers — baby teeth, otherwise known as deciduous or primary teeth. 

Because the mouth of a toddler doesn’t hold enough space for all 32 teeth, these 20 primary teeth sort of act as “reserved” signs at a theater, saving space in the mouth for when those permanent teeth are ready to emerge. As with adult teeth, baby teeth also help children learn to speak, serving the same structural role for forming the basic phonetics that make up language.

Given such an important role baby teeth play in our development, we might need to up the Tooth Fairy’s asking price.

At the first sneeze and sniffle of cold season, get ready for a few inevitabilities ahead of you. Tossing and turning at night? Check. A mountain of tissues piled up on your nightstand? Check. Every meal until you feel better tasting blah? That too. 

When a head cold hits, even your grandma’s famous chili recipe may suddenly taste like flavorless mush. You might pick up on a hint of saltiness from the beans or sweetness from the tomatoes, but the layered, savory richness you normally crave a bowl (or two) of is gone.

That’s because your tongue is only partly responsible for what you experience as flavor.

Tasting With Your Nose

Your tongue detects five basic tastes: sweet, salty, sour, bitter, and savory (umami). Flavor, however, is a much bigger sensory experience, much of which is built in your nose. That’s why you can immediately know what to expect when walking into a steakhouse or an Italian restaurant without having to lick the walls. 

In fact, smell is responsible for as much as 80% of what we perceive as flavor, according to smell and taste researchers. 

Your nose contributes to flavor in two ways. The first is orthonasal olfaction, which is a fancy way of describing what happens when you smell something through your nostrils before eating it. That’s the aroma you notice when you sniff a pile of pancakes, for instance.

When you’re eating those pancakes, a second pathway called retronasal olfaction kicks in. As you chew and swallow, you’re not just cutting your food up into smaller bites to swallow — you’re also breaking it down on a microscopic level, allowing tiny odor molecules to escape. 

These molecules travel from your mouth up through the pharynx (the back of your throat) and into the nasal cavity. There, they reach the olfactory epithelium, a patch of tissue containing the nerve receptors that detect smells. Your brain combines that information with the basic tastes coming from your tongue to create the perception of flavor.

Nasal congestion severs that connection. Swollen nasal tissue and excess mucus clog the passage, so air — and the odor molecules along for the ride — can’t circulate up the back of your throat. Your tongue can still detect the five basic tastes, but without as much information from your nose, the brain has fewer sensory details to work with.

Think of it like a band missing half its instruments. The tongue is the rhythm section, laying down a steady beat: sweet, sour, salty. The nose supplies the complex melody; it’s the strings and horns that make a song memorable. Block the nose, and all you’re left with is the basic beat.

When smell is impaired, your brain compensates by relying more on the somatosensory system to receive information about what you’re eating. Somatosensory nerves detect stimuli such as touch (texture), temperature, and pain. 

That’s why chemical irritation caused by certain foods, such as the burning sensation from chili peppers or the cooling snap from mint, may still have some kick when you’re congested. Those sensations can’t replace flavor, but they can help a bland meal taste a little less flat.

So when you’re treating your cold with chicken soup, feel free to add a dash of chili powder.

You stand up a little more carefully than you used to. The music in a crowded cafe seems louder and the conversation across the table gets harder to hear. Nutrition labels become more difficult to read. Aging often arrives not as one dramatic event, but as a collection of tiny surprises like these. It can be tempting to think of these changes as evidence that the body is simply wearing out, but that’s only part of the story. 

From the moment we’re born, our cells are constantly growing, repairing, replacing, and adapting. As the decades pass, those repair systems become a bit less efficient. The good news is that most age-related changes happen gradually, giving our bodies plenty of time to adjust.

And while aging is inevitable, many of its effects can be slowed — or at least softened — through proper exercise, nutrition, sleep, and medical care. Here are 10 of the most common changes that happen as we grow older.

Your Heart Works Harder

Your heart is an incredibly durable organ, pumping billions of times over the course of a lifetime. As the years pass, however, your arteries gradually become thicker and stiffer, making it harder to push blood through them. In response, the heart muscle itself must work harder to do its job.

Interestingly, your resting heart rate usually stays about the same. The bigger change is that your heart doesn’t speed up during exercise quite as readily as it once did, which means your muscles are not getting the additional oxygenated blood they need for energy. This is one reason climbing a steep hill may feel more challenging than it did decades earlier.

Your Bones Lose Mass

Until about age 30, your skeleton is busy building bone faster than it loses it. After your third decade, the balance gradually shifts, and bone breakdown starts happening more quickly than bone formation. Your bones become less dense and more susceptible to fractures. It’s also one of the reasons we often seem to magically shrink as we age. Strength training (even gentle exercises such as walking) can help slow some of these changes, however.

Your Eyes and Ears Become More Selective

If reading tiny font sizes (like those darn package labels) has become more difficult, you’re in good company. As we age, the lens inside the eye gradually thickens and loses flexibility, making it harder to focus on objects close to us. Many people also become more sensitive to glare and need more light for reading. Even those with decades of perfect vision may soon be keeping a pair of reading glasses on the end table.

Our hearing also changes with age. The small, delicate cells inside the inner ear decline over time because, no matter what your age, they don’t regenerate once damaged (yet another reason to wear earplugs during rock concerts). Because the cells that absorb high-pitched noises tend to wear out first, these sounds are the ones that often become more difficult to detect as we age. That’s why birdsong or children’s voices may become harder to distinguish as we age, even when overall hearing still seems fairly strong.

Your Skin and Hair Slow Down

Your skin tells your life story: whether you lived in a sunny climate or not, for instance, or how much you’ve laughed or frowned. But no matter what your lifestyle, skin produces less collagen, elastin, and natural oils as you age, becoming thinner, drier, and less elastic. Fat beneath the skin also decreases, making bruises more common and wrinkles more noticeable. On the plus side, our sweat glands become less active as we age, which might at least save some money on deodorant.

Gray hair follows a similar trajectory. Hair follicles gradually stop producing melanin, the pigment that gives hair its color, leaving strands silver, white, or gray. Nails often grow more slowly as well, though in some people they can remain long and strong well into old age.

Your Brain Works a Little Differently

Forgetfulness is one of the changes people fear most, but there’s a difference between your brain naturally slowing down and dementia, which is a condition that’s not considered a normal part of aging. Healthy seniors may take a little longer to retrieve a name, learn a new technology, or remember where they left the car keys. Processing speed often slows somewhat, as the connections in your brain cells slow and decrease.

Perhaps more encouragingly, the aging brain remains capable of learning throughout life. You can teach an old dog new tricks, even if it takes a bit longer to perform them. Although it may take longer to master new skills or retrieve information, the brain continues to adapt and reorganize itself in response to new experiences. There are some cognitive pluses to aging, too — for one thing, older adults tend to have larger vocabularies.

Your Digestive System Takes Its Time

Just as it might take us a bit longer to walk to the kitchen, our digestive tract also slows down as it ages. Food generally moves more slowly through the digestive tract, and the stomach, liver, pancreas, and intestines may produce fewer digestive juices. The result can be constipation or slower digestion, especially when combined with reduced physical activity, certain medications, or a lower-fiber diet. Fortunately, many of these changes respond well to simple habits such as staying active, drinking enough water, and eating plenty of fiber.

Your Metabolism Changes

Many people notice that maintaining the same weight becomes more difficult with age. That’s partly because metabolism gradually slows, but muscle loss also plays an important role. Muscle tissue burns more calories than fat, so as muscle declines, the body naturally uses less energy. The encouraging flip side is that regular physical activity helps preserve muscle, keeping metabolism higher than it would otherwise be.

Your Immune System Can be Less Responsive

The immune system doesn’t retire, but it does become somewhat less responsive over time. The body produces fewer of certain immune cells, making it slower to recognize and fight off infections. This is one reason older adults are encouraged to stay current on vaccines, which help give the immune system a helpful preview of viruses it may encounter. Researchers are actively studying ways to better understand — and perhaps slow — these changes as life expectancy continues to increase.

Your Bladder Loses Some Patience

If bathroom trips seem more frequent than they once were, aging may be partly responsible. The bladder gradually becomes less elastic and can’t hold quite as much urine as it once could. Meanwhile, the muscles that help control urination may weaken, making leaks more common for some people.

While these changes are widespread, they’re not something people simply have to live with. Pelvic floor exercises, lifestyle changes, and medical treatments can often make a significant difference.

Your Body Keeps Adapting

Perhaps the most surprising thing about aging is that our bodies don’t simply decline — they continually adjust. The heart compensates for stiffer arteries. The brain develops new pathways. Muscles respond to exercise at almost any age. Bones remain living tissue that constantly rebuild themselves.

Growing older certainly brings changes, but it also reveals something extraordinary about the human body: even after decades of use, it never entirely stops repairing, adapting, and finding new ways to carry us through the world.

Air travel can be a real hassle these days. You pay exorbitant fees for frequent delays, ever-shrinking legroom, and fewer, if any, free snacks — not to mention battling your neighbor for the armrest. On top of all that, flying can put your body through the wringer due to pressure changes and other environmental factors, affecting everything from your taste buds down to your very DNA. Here are some surprising physiological changes that happen to your body when you fly.

Your Taste Buds Go Haywire

Ever notice how food often tastes different on planes? If a particularly nice flight attendant lets you grab pretzels and cookies, you may find both to taste a bit bland. Scientists have confirmed that, for most of us, our taste buds’ ability to detect salt and sweetness is suppressed during air travel.

On the flip side, savory umami flavors — such as frequent flyers’ beloved tomato juice — are accentuated. Airlines aren’t skimping on sugar, though. It’s not the actual airplane food, but the airplane noise that affects your taste buds. 

In 2015, Japanese researchers discovered that noisy environments alter our sense of taste, and the loud 85-decibel ecosystem of an airliner boosts savory flavors. So remember that if you use noise-canceling headphones on your next flight, you may also be using taste-cancelling headphones.

Your Feet Swell

The longer the flight, the tighter your shoes feel. Foot swelling is one of the most common side effects of flying, and has more to do with being sedentary than with the flight itself. Because of gravity, sitting in a cramped seat with your feet planted on the floor for long stretches causes blood to pool in your leg veins. Over time, fluid seeps from the blood into surrounding tissues, causing swelling.

This would happen whether you sat upright without moving all day on an airplane or in your own home. Usually, this is harmless, but certain people with preexisting health conditions may be at risk of complications such as deep vein thrombosis. That’s why it’s a good idea to stretch and walk up and down the aisle every so often. You should also consider wearing a well-made pair of compression socks for flights longer than four hours, as they help prevent pooling by applying a bit of pressure to your calves. 

Your Ears Pop

You almost certainly know this one. The pilot says, “Prepare for takeoff,” over the intercom. The flight attendants take their seats. Your stomach sinks as the plane takes off, and the next thing you know, your hearing becomes muffled and your ears start popping. 

Airplane ear, or ear barotrauma, occurs when air pressure inside the cabin gradually decreases as the plane gains altitude. Air trapped inside your inner ear exerts pressure on your eardrums, pushing them outward, which can be very uncomfortable. Fortunately, your body can actively try to relieve this discomfort all on its own — this is why your ears pop on airplanes. By releasing air via the Eustachian tubes, your body balances the pressure inside your ear, not unlike “burping” a Tupperware lid.

You Get Gassy

No matter how short the flight, air travel probably makes you feel a little uncomfortable, and not just because of your coughing seatmate. Flying creates bloating — and even flatulence. The decreased air pressure that makes your ears pop also causes the gas in your digestive tract to expand. Couple that with increased water retention that also often occurs during travel, and you’ve got a recipe for mile-high toots.

You Get Dehydrated

It may feel as though no matter how many cups of water you down during your flight, you feel parched when you land. This happens because airplane cabins are extremely dry, with most averaging just 5-12% humidity. To put that in perspective, the Sahara Desert averages around 25% humidity, meaning your airbus is drier than the largest desert on Earth.

The low humidity is caused by high-altitude air — roughly 50% of the air circulating in a cabin is drawn from the outside. At 35,000 feet, water vapor is scarce and the air is bone dry. This doesn’t just make you thirsty, but will also dry out your skin, which is why you may find yourself reaching for the lotion when you land.

Your Blood Oxygen Levels Drop

When you think of hypoxia, or oxygen deprivation, you probably imagine mountaineers scaling Everest. But altitude sickness can happen during air travel, too, as the air pressure in a plane cabin is equivalent to what you’d experience at an altitude of around 7,000 feet.

This can drop your blood oxygen levels and, in extreme cases, cause hypoxia. It’s rare, but people with preexisting conditions, such as heart or lung trouble, are more vulnerable. Then there are also those little bottles of free booze some airlines hand out: A 2024 study found that the blood oxygen level of people who had consumed alcohol and slept in lower air pressure environments dropped to as low as 85% — well below the ideal range of 95-100%. 

You Get Jet Lag

If you ever travel eastward on a transpacific flight, you could theoretically depart Asia on a Monday afternoon and land in North America the previous Sunday morning. This faux time travel happens when you cross the international date line, and it’s the perfect recipe for jet lag. Jet lag is more than being tired or even confused because your watch is wrong — it’s a real biological condition.

A California-bound flight from Japan is an extreme case, but jet lag can get you on much shorter trips, too — traversing just three time zones will throw your circadian rhythm off. Your body relies on your internal clock more than you might think, and jet lag can affect the way your cells function or even how your genes are expressed, disrupting your immune system and other bodily functions. Even the way you process certain medications can change while you’re jet-lagged.

Thankfully, there are many tricks for combating this, ranging from adjusting sleep patterns in advance to avoiding alcohol and sticking to small meals during travel.

You’re Dosed With Cosmic Radiation

Bet you didn’t have cosmic radiation exposure on your bingo card. Just as the legendary Icarus discovered, flying closer to the sun does come at a cost (in addition to those outrageous airfares). Every second of every day, Earth is bombarded by solar radiation from the sun and cosmic radiation from the rest of the universe. Fortunately for us, our planet’s atmosphere and magnetic field keep that radiation from doing much damage to us on the surface (outside of the occasional sunburn, perhaps.)

But the atmosphere is much thinner at high altitudes, exposing your body to a much greater amount of cosmic radiation. The length and altitude of a given flight determine the dose of radiation you can expect to receive. Thankfully, even the highest doses are still pretty low. For example, two transcontinental flights across the U.S. expose you to the equivalent of radiation from a single chest X-ray. 

So, no need to cancel that trip to Greece — unless you’re planning on flying with wax wings, that is.

It almost seems as if your stomach deliberately waits to growl until you’re in a meeting, watching a movie, or in some other quiet situation where everyone around you can hear. You haven’t eaten in a while, sure — but you’re not even that hungry.

That’s because a growling stomach doesn’t always mean it’s mealtime. So if your belly isn’t telling you it’s hungry, why does it sound so angry sometimes?

The Sound of Digestion

Those noises have a name: borborygmi. It’s not actually a growl, of course. It comes from movement inside your stomach and intestines, where muscles squeeze in rhythmic waves to push food, liquid, and gas along. Imagine a tube of toothpaste that could squeeze itself to push its toothpaste out — that’s essentially your digestive system. 

When that gas and fluid get shoved around inside a mostly empty digestive tract, you get the gurgle. Food tends to muffle those contractions. That’s why an empty stomach tends to be the noisier one — there’s less material inside to absorb the sound, not necessarily more happening inside.

But hunger isn’t a requirement for the sound. Between meals, your stomach and small intestine cycle through something called the migrating motor complex — basically a maintenance mode for digestion. During these periods of fasting, waves of stronger contractions move through the digestive tract, helping move leftover material and digestive secretions along. Think of it as a broom sweeping through after dinner, even though the restaurant has already closed.

Researchers studying fasting volunteers found that gut sounds became more pronounced during the more active phases of this cycle, when contractions were stronger and more frequent.

That same digestive activity is why your stomach can growl after you eat, too. The influx of food may help absorb stomach noise, but it also increases digestive activity since there’s a whole new meal to digest. Your intestines keep contracting, mixing and moving food along, sounds included.

Not everyone’s stomach is equally chatty, either. Some people also swallow more air while eating or talking, which gives those digestive contractions more gas to move around and can contribute to the sounds you hear. (So chewing with your mouth closed isn’t just manners — it has actual physical effects.)

A full stomach can rumble plenty. An empty one can stay dead quiet. The sound itself isn’t a reliable measure of hunger; it’s simply the audible result of what’s happening inside your digestive tract.

Next time your stomach speaks up in a silent room, it’s probably not asking for a snack. It’s just doing its regular digestive work — and making sure everybody knows about it.

Watch a toddler settle in for a car ride, nap, or story time, and odds are a thumb finds its way into their mouth within minutes, if not seconds. It’s one of those habits that seems to come out of nowhere and then just… stays around, sometimes for years.

But there’s actually a reason kids gravitate toward this behavior. And it starts long before the toddler stage — before birth, actually.

A Habit That Forms While We Do

Before a baby can even see or hear, they may start sucking their thumb. Ultrasounds have caught fetuses in the act as early as 14 weeks into pregnancy. It’s not just random movement, either. 

Sucking is a natural reflex that develops before birth, and practicing may help prepare babies for feeding after they’re born. A newborn has to coordinate sucking and swallowing right away, so there’s a fair amount of rehearsal happening before anyone gets to hold them.

But, clearly, the habit can linger long after a baby learns to feed and even eat solid foods. That’s because the same reflex takes on another job that has nothing to do with getting fed. Doctors call it non-nutritive sucking, and it’s one way babies calm themselves. 

Sucking can settle a crying infant, help with sleep, and reduce responses to pain. In one study, newborns given a pacifier during a blood draw showed lower pain responses than babies who didn’t receive one. That’s part of why pacifiers are sometimes used to comfort newborns during minor procedures, whether they’re hungry or not.

A thumb has one very practical advantage over a pacifier: It’s attached to the body. Nobody has to find it under the crib at 2 a.m. It’s also the easiest of the five fingers to access without contorting your wrist. Once a baby discovers that sucking feels comforting, there’s always a soothing tool right there, wherever they are, whenever they’re tired, cranky, bored, or trying to settle down.

Most kids eventually stop. As they get older, they have more ways to entertain and comfort themselves, and the thumb gradually becomes less interesting. For some children, that happens without anyone having to intervene at all.

The part dentists care about is what happens if the habit sticks around. Occasional thumb-sucking isn’t generally a problem, but frequent, vigorous sucking can put enough pressure on the developing mouth to affect the position of permanent teeth or even the shape of the roof of the mouth. That’s why the American Dental Association recommends addressing thumb-sucking habits that persist as permanent teeth begin to come in.

That doesn’t mean a preschooler with a thumb in their mouth is definitely headed for dental trouble. The timing and intensity of the habit matter. A child reaching for a thumb at bedtime isn’t necessarily a red flag. They’re simply using a soothing reflex that has been part of their repertoire since before they were born. 

Eventually, most find something else that works. Just as with toys and plenty of other things, many kids just get bored with the habit.