Olivia: Happy New Year! Whether you watched the ball drop, set off fireworks, or baked money into pies, we all have our New Year's traditions. And often those traditions involve popping a bottle of champagne and toasting the new year. So, to ring in 2017, here are some of our favorite SciShow videos on the Science of alcohol.

First, if you partied a little too hard last night, don't worry, here's Hank with the science of hangovers.

Hank: What do fried canaries, pickle juice, Coke mixed with milk, Vegemite, boiled tripe and coffee have in common? Well in addition to being frickin' nasty, except for the coffee, they're all purported folk remedies for a hangover.

Most adults who partake of alcohol have experienced at least one, or two, or three, or fifty dozen hangovers in their lives, and by all accounts it sucks. Terrible headaches, nausea, fatigue, dizziness, that feeling of your eyeballs wanting to fall out of your head. But how does this stuff work?

Well, it involves three really miserable interacting things. The first step of the hangover is the biggest cause of your misery: dehydration. Booze is a diuretic which means it makes you have to pee, which is why there is always a line at the bathroom in a crowded bar.

Alcohol suppresses the pituitary gland's release of vasopressin, the hormone that triggers the re-absorption of water back into the body. Without it, the kidneys just send the water straight to your bladder and into the john.

Headaches follow when the body desperately resorts to stealing water from the brain, causing the tissues to shrink and pull away from the skull. Meanwhile, all that peeing causes you to lose a lot of sodium, potassium and magnesium which are all necessary for proper cell function.

Step two: acetaldehyde overload. Our bodies metabolize alcohol in two phases. First, liver enzymes break down the actual alcohol in the drink, called ethanol, which creates a toxic byproduct called acetaldehyde. The acetaldehyde is then attacked by more enzymes and a peptide called glutathione and is soon reduced to harmless acetate.

This works fantastically if you're drinking small amounts. But if you're guzzling pints all night, eventually your exhausted liver can't keep up and all that toxic acetaldehyde starts to build up making you feel really crappy.

Step three: the congener connection. In addition to alcohol ruining your body's ability to hold water and creating toxic leftovers for your liver to handle, most drinks also contain congeners. In chemistry, this refers to any group of related chemicals. But in this case, when we're talking about alcohol, it has to do specifically with chemical impurities that form during fermentation and aging of alcoholic drinks.

They provide flavor and color, but they also contain some of the same toxins that give your liver trouble, like acetaldehyde, esters and acetone, aka paint thinner. Darker drinks like brandy, bourbon and red wine have more congeners than clear spirits like vodka and gin. But, if you're over 21 and currently hungover you don't need me to tell you why you're experiencing such a terrible experience, you just need me to tell you how to make it stop.

Fact is, none of the above remedies I mentioned earlier are going to help. Coffee may help relieve a headache by shrinking the blood vessels in your head but it will also continue to dehydrate you. And don't reach for the hair of the dog, because that just prolongs the inevitable.

Replenishing sugars and minerals with a sports drink or a nice healthy banana isn't a bad idea, but if you ask any doctor they'll tell you the only sure cure for a hangover is time. It's time the afflicted can spend re-hydrating, eating, sleeping and thinking about making better choices. And of course, the one foolproof way to avoid a gnarly hangover: don't drink so much.

Olivia: SO happily, with time and maybe some coffee, you'll recover from a hangover. But does alcohol kill brain cells? Here's Michael with that answer.

Michael: The claim that alcohol kills brain cells dates back to the temperance movement of the early twentieth century, when Prohibition advocates wanted to make alcohol illegal in the United States. These people, who warned that a couple of gin rickeys would eat away your brain were the same ones that also circulated claims that, say, alcoholics could catch fire and burn alive because of all the alcohol in their blood. Neither claim is true, I'm happy to report, although parents and teachers have repeated the first one enough over the last century that it's often passed off as fact.

Very roughly speaking, your brain has about 100 billion nerve cells called neurons, and the active ingredient in intoxicating beverages is ethyl alcohol. When you drink it, it's processed by your liver where it's metabolized into acetate and eventually eliminated.

But if you drink too much alcohol too quickly, your liver can't process it fast enough, so the excess alcohol stays in your blood and reaches the brain. Once there, alcohol disrupts your brain function by damaging the connective tissue at the end of those neurons, called dendrites. While the cell itself isn't killed, the damage to the dendrites interrupts communication between your neurons, making it harder to send messages that have to do with things like learning or motor coordination. This is what causes the effects we often associate with being drunk, like stumbling, slurred speech and making, what in hindsight often prove to be really bad decisions.

But we know the brain cells don't actually die thanks to a study done in 1993, in which scientists actually counted the neurons in brain samples from alcoholics and non-alcoholics. They found no difference in the total number of neurons, and these findings have been confirmed by other recent studies.

Luckily, the damage done to our dendrites during an evening of drinking is almost always reversible, and if you stop drinking for long enough, the brain will repair itself. But, of course, drinking alcohol in large quantities poses many, many other health risks, and while it may not kill brain cells, it can greatly impair brain function and permanently damage your poor liver.

Olivia: OK, so alcohol doesn't kill brain cells. But that's not the only old saying about alcohol that might not be true. You've probably heard somewhere that alcohol can keep you warm, but is it true? I mean some alcohol definitely burns when you drink it, but is that really warming you up? Well here are a couple of videos that answer those questions.

Michael: You may have seen pictures of St. Bernards carrying little kegs of brandy around their necks to keep stranded hikers from freezing to death, but does alcohol really keep you warm?

Not only is the answer here a definite no, but in fact the opposite is true. While alcohol may make you feel warm, it actually makes you colder. Alcohol causes your blood vessels to expand in a process called vasodilation. This allows your blood to rush to the surface of your skin, where most of your nerve endings are. Since your blood is all warm and toasty, a flood of blood into the dilated capillaries means that you feel a rush of heat.

But that heat is coming from your own body's core temperature, so when your blood rushes to your skin, which is in contact with the colder air, that heat rapidly dissipates and causes your body temperature to drop. That's why your capillaries were actually constricted in the first place, to stop your blood from rushing to the surface; that's one of your body's only ways of protecting you from the cold and stopping you from freezing to death.

And here's another reason you might want to reconsider taking a swig from your flask when you're in the chair lift or whatever. If you've wondered about the burning sensation you feel in your mouth and throat when you partake, it's because the alcohol tinkers with the nerve receptors that you use to detect heat.

When these receptors, which are heat activated proteins called TRPV-1, come into contact with alcohol, their threshold for detecting warmth actually drops from 42º C to 34º, lower than your body temperature. So the burn that you feel when you drink is actually just you, you feel like you're getting scalded but what's really happening is that your nerve cells have suddenly just become extra-sensitive to your own body heat. Just when you thought alcohol couldn't get any more interesting.

But long story short, if you're trying to stay warm when it's cold out, skip the brandy and the schnapps and go straight for the hot chocolate.

Hank: If you’ve ever tasted anything with alcohol in it, you know that it can burn on the way down. In the extreme -- like, if you down a shot of everclear or something -- it might even feel like your mouth and throat are being scalded. Maybe your eyes start watering, and your nose starts running... it was supposed to be a casual swig, and now all your fellow drinking-aged friends are laughing at you.

But there’s a good reason that alcohol burns so much, and it has nothing to do with its actual temperature. Instead, that shot of tequila feels hot because it’s messing with a type of heat receptor in your mouth and throat -- specifically, the receptor called VR1. When you taste something with a high temperature, it triggers this receptor, which sends a message to your nerves that they’re detecting something hot. That message then gets sent along to your brain, and you feel it as burning and probably pain.

Ethanol -- the kind of alcohol that’s relatively safe to drink -- binds to those same receptors. And so does capsaicin, which you might know as the stuff in spicy food that makes your mouth feel like it’s on fire. But capsaicin activates those receptors directly, telling them that wow, that chili is REALLY HOT, whereas ethanol just makes them more sensitive.

Normally, your VR1 receptors activate at 42 degrees Celsius -- in other words, anything warmer than 42 degrees feels hot. But ethanol lowers that threshold to just 34 degrees. And your body temperature? That’s around 37 degrees. So, suddenly, your body feels like it’s burning you. Alcohol is just weird, people. So the next time you take a shot and your eyes start watering, just remember: it’s not the booze that’s hot. It’s you.

Olivia: So that settles it, alcohol doesn't heat you up, but alcohol definitely makes you pee. Why? Well, here's Hank to explain, and it's a lot more complicated than you might think.

Hank: Here’s a question that a lot of people have asked the internet, presumably after a party, or during a lull in a wedding reception, or maybe around last call at the local tavern if their fingers, they can get them to work on the phone... Why does beer make you pee?

Well, you know how alcohol tends to make simple things suddenly really complicated? Well, that applies here, too. You might think that the answer is obvious: beer goes in, pee comes out. Beer is mostly water, so why wouldn’t it make you pee? But, it’s a little more complicated than that, and it has to do not just with beer, but any drink that has the active ingredient ethanol, also known as ethyl alcohol.

You probably know that alcohol messes with all sorts of brain functions—just first-hand, probably. It does this by making it harder for your neurons to communicate with each other, but it also affects your endocrine system, that network of glands that secretes the hormones your body needs to keep your heart beating and your cells metabolizing and your sexy parts working.

In this case, alcohol interferes with a specific hormone secreted from your pituitary gland called vasopressin, sometimes called anti-diuretic hormone. Its job is to help your body retain water. It sends signals to your kidneys to keep your body hydrated by maintaining just the right balance of water and mineral salts in your blood.

But while the alcohol’s messing with your brain, it’s also messing with your pituitary, and actually turns off the production of vasopressin. Without those orders being sent to your kidneys to retain a certain amount of water, they just start letting all the water in your system through, sending it straight to your bladder.

So the more alcohol you ingest, the less vasopressin you produce, the more water you lose. That is why after a couple of drinks you’ll notice that your urine becomes lighter in color, and if you’ve had way too much, eventually comes out clear. At that point, you’re essentially peeing out nothing but water. When you see that, you know that you’ve not only had too much, but you’re in for a hurtin’ the next day, because dehydration is what causes hangovers.

Olivia: So alcohol can cause hangovers, it can trick you into thinking you're warm, and it definitely makes you pee, but there are other more long-term effects and een dangers that alcohol can have on a person's body. Here's Michael talking about the science and dangers of booze in humans.

Michael: Ah, alcohol. It's known to make people all around the world feel a little more outgoing at dinners and dance parties. But the inside of your body sees alcohol as a poison, and it tries to get rid of it ASAP. Whatever your body can't process right away can end up in your brain, which affects how your cells interact with each other and causes all those things that we associate with drunkenness. So it's totally fine to have a beer or two with your drinking-aged friends. But consistently drinking way too much alcohol can get dangerous in the long run.

When you take a sip of an alcoholic beverage, the toxic stuff it contains, ethanol, also known as ethyl alcohol, is absorbed into your bloodstream through your stomach lining or small intestine. Your liver is responsible for filtering out this ethanol and breaking it down, using enzymes and other peptides, so your body can safely get rid of it.

First it's converted into acetaldehyde, which is toxic too and probably a big reason for those nasty hangovers. Then, another enzyme turns acetaldehyde into acetate, which is harmless and eventually excreted in urine. And your liver does its best to get rid of all the ethanol you're putting in your body. But if you keep refilling that wine glass, it has trouble keeping up. So any excess ethanol circulates in your bloodstream and eventually reaches your brain.

Now, usually, foreign substances like bacteria and toxins are kept out of your brain thanks to the blood-brain barrier, basically a filter made of specialized cells and proteins. But it's actually pretty easy for ethanol to get in, because it's attracted to fats, so it can pass through those fatty cell membranes. And once alcohol reaches the brain, it starts to mess with the signaling between neurons – aka brain cells.

The brain uses these chemicals called neurotransmitters to send messages between cells. The two most important ones are γ-aminobutyric acid, or GABA, and glutamate. GABA binds to specialized receptor proteins and causes neurons to send fewer signals so scientists say it's an inhibitory neurotransmitter. Glutamate, on the other hand, binds to receptors and causes neurons to send more signals so it's an excitatory neurotransmitter.

Ethanol interferes with this signaling by binding to both of these receptors, and changing the messages the neurons receive. Specifically, ethanol enhances GABA signaling and reduces glutamate signaling, which means there's more inhibitory signaling and slower brain activity overall. That's why alcohol is considered a depressant.

And its effects on different brain regions can cause different symptoms of drunkenness. For example, alcohol reduces activity in the cerebellum, which is responsible for motor coordination – causing all of that stumbling. It also suppresses the areas of the brain responsible for self-control and social inhibition, which makes us more outgoing, emotional, and prone to risky decisions.

These effects go away as your body continues to process the ethanol. And as far as we know, there aren't serious risks to moderate alcohol consumption. But ethanol is a toxin. So if you keep downing drink after drink in a short period of time, you can get alcohol poisoning – basically, a shutdown of the medulla, which is the brain region that manages vital life support functions, like breathing and heart rate.

And there are long-term dangers linked with excessive amounts of alcohol consumption. You can get liver cirrhosis, or seriously scar your liver tissue, because it gets damaged and doesn't work as well trying to process so much toxin for so long.

Scientists also think a lot of ethanol in your bloodstream can put stress on other tissues in your body too leading to inflammation, interfering with normal hormone levels, and making it harder for your cells to repair their DNA, all of which can increase the risk of developing certain cancers. And even though alcohol doesn't kill brain cells, too much alcohol can also have long-term effects on the brain.

There's some evidence that consistently drinking alcohol as a young teenager can impact the growth and maintenance of connections between neurons, sometimes leading to learning and memory problems.

Alcoholism is a physical dependence on alcohol, characterized by cravings for booze and the inability to stop drinking once you've started. Scientists also think too much ethanol in the bloodstream over a long period of time could prevent our intestines from properly absorbing thiamine, or vitamin B1, and make it harder for our livers to store and use it, too.

A thiamine deficiency can lead to Wernicke-Korsakoff Syndrome which is associated with the damage or shrinkage of several brain regions, and causes a lot of problems in movement, memory, and vision. So a lot of really serious, unpleasant stuff.

Alcohol has a lot of effects on the human body, and because it's a toxin, drinking too much can lead to some serious health concerns. But in moderation – around one or two drinks per day – it's considered to be fairly safe. So drink responsibly, friends.

Olivia: Yes, as Michael said, drink responsibly! And if you're thinking you're ready for a drink right now, prepare your drink with science! Here's one more video with Hank explaining the best and most scientific way to pour a good beer.

Hank: Beer. It's refreshing, delicious, bubbly, tingly and full of chemistry. We've talked about the science of making beer, but there's also a science to the way we pour beer. You probably know the drill: always tilt the glass. But why? It's all about the foam.

Beer has lots of dissolved carbon dioxide - the same stuff that gives soda its bubbles. This CO2 is created during the fermentation of sugar by yeast cells - the process that also produces the alcohol.

When you first crack open a can or bottle of beer, that whooshing sound you hear is the pressure inside the container dropping to match that of the outside world. In the process, a little bit of CO2 is released but most of it stays trapped in the liquid. And when you tilt your glass while you pour your beer, you're stopping most of the remaining gas from escaping.

See, the carbon dioxide in the beer wants to come out, but it needs help - the molecules needs a place to come together in order to create bubbles. These spots are called nucleation sites. Have you ever watched as, like, a string of bubbles pop out of, like, one single place on a glass? That's a nucleation site - it could be a fiber or dust particle on the glass, an imperfection or bump, or even a tiny trapped air bubble.

And that's what you're trying to avoid by tilting your glass while you pour your beer: trapped air that can then turn into nucleation sites. If you pour your beer straight in, without tilting, you're forcing a bunch of air into the beer, providing lots of those little nucleation sites and helping the CO2 escape. As the gas rises, it gets coated in proteins from the grain, which can provide enough surface tension to keep the gas trapped in bubbles on top of the beer.

That's what makes the foam on the top - also known as the head. Since you probably don't want a cup full of foam, when you pour your beer in you need to control the release of the CO2 and the formation of the head. A gentle pour down the side of the glass traps much less air, which means fewer nucleation sites, which means more carbon dioxide stays in the liquid where it belongs. In other words: less foam, more tingly.

At the very end of your pour, you can stop tilting the glass - that way you end up adding a few centimeters of head to the top of your beer. Because having some foam can be a good thing! It helps you smell the beer while you're drinking it. You just probably don't want too much of it.

And it turns out this tilting method works for more than just beer. French scientists at the University of Reims found that tilting that glass is also the best way to pour champagne in order to preserve the bubbly bite of the drink. Cheers French scientists!

Olivia: Thanks for watching this special New Year's Day compilation and helping us cheers in the new year with the science of alcohol. If your New Year's resolution is to continue getting smarter, make sure you go to youtube.com/scishow and subscribe.