New Year's Eve is around the corner. For many of us, that means staying out late, dancing and drinking.

Thus, for some of us, the night of carousing also means a morning of hangovers.

Just in the nick of time, here's our complete guide to the science of hangovers—what we know, what we don't know, and how you can use this information to minimize your suffering.

Why Do Hangovers Happen?

Given that they're such a widespread health phenomenon, it's perhaps a bit surprising that scientists still don't fully understand the causes of a hangover. (They do, however, have a scientific name for them: veisalgia.) It's far from clear why, after all traces of alcohol have been fully expelled from your body, you can still experience a load of awful symptoms, including headache, dizziness, fatigue, nausea, stomach problems, drowsiness, sweating, excessive thirst and cognitive fuzziness.

The simplest and most familiar explanation is that drinking alcohol causes dehydration, both because it acts as a diuretic, increasing urine production, and because people who are drinking heavily for multiple hours probably aren't drinking much water during that time period. But studies examining the link between dehydration and hangovers have turned up some surprising data. One, for instance, found no correlation between high levels of the hormones associated with dehydration and the severity of a hangover. It's most likely that dehydration accounts for some of the symptoms of a hangover (dizziness, lightheadedness and thirst) but that there are other factors at work as well.

Most scientists believe that a hangover is driven by alcohol interfering with your body's natural balance of chemicals in a more complex way. One hypothesis is that in order to process alcohol, your body must convert the enzyme NAD+ into an alternate form, NADH. With an excess buildup of NADH and insufficient quantities of NAD+, the thinking goes, your cells are no longer capable of efficiently performing a number of metabolic activities—everything from absorbing glucose from the blood to regulating electrolyte levels. But this hypothesis, too, has been contradicted by data: In studies, people with severe hangovers weren't found to have lower levels of electrolytes or glucose in their blood.

The most compelling theory, at the moment, is that hangovers result from a buildup of acetaldehyde, a toxic compound, in the body. As the body processes alcohol, acetaldehyde is the very first byproduct, and it's estimated to be between 10 and 30 times as toxic as alcohol itself. In controlled studies, it's been found to cause symptoms such as sweating, skin flushing, nausea and vomiting.

Hangovers could also be driven by the way alcohol messes with your immune system. Studies have found strong correlations between high levels of cytokines—molecules that the immune system uses for signaling—and hangover symptoms. Normally, the body might use cytokines to trigger a fever of inflammatory response to battle an infection, but it seems that excessive alcohol consumption can also provoke cytokine release, leading to symptoms like muscle aches, fatigue, headache or nausea, as well as cognitive effects like memory loss or irritation.

Why Do Some People Get Hangovers More Easily?

Life, alas, isn't fair. Some people are extremely prone to hangovers, and some can drink with impunity.

It seems that genetics are partly to blame. Some people (disproportionately those of East Asian descent) have a mutation in their gene for the enzyme alcohol dehydrogenase that makes it much more effective in converting alcohol into the toxic acetaldehyde. Unfortunately, a significant part of this group also has a mutation in the gene for the enzyme that performs the next metabolic step, leading to a much slower conversion of acetaldehyde into acetic acid. As a result, excess buildup of acetaldehyde can happen quite rapidly. This is known to cause an immediate alcohol flush reaction (colloquially known as "Asian glow"), but might also play a role in hangovers the day after drinking.

There are other factors that affect who experiences hangovers most readily. After having the same number of drinks, women are more likely to experience hangovers than men, though this simply seems to be a result of the fact that women generally have a lower body weight as well: If you control for body weight and compare a man and woman with the same blood alcohol content, their chances of a hangover are similar.

There's conflicting evidence over whether hangovers become more frequent with age. Some studies have suggested [PDF] that adolescents are less likely to experience hangovers, but a recent large-scale survey showed the opposite—that, even controlling for total alcohol consumption, drinkers over the age of 40 experienced fewer and less severe symptoms. The authors noted that it's possible, though, that they consume the same amount of alcohol but with less intensity, spreading their drinks out instead of binging.

Why Do Some Drinks Cause Hangovers More Easily Than Others?

Because the ultimate cause of a hangover is, after all, alcohol, drinks that pack more alcohol into a smaller volume are naturally more likely to give you a hangover. Shots of liquor, in other words, are more dangerous than mixed drinks, beer or wine.

Beyond that, though, some drinks happen to have higher levels of congeners—traces chemicals produced during fermentation—that contribute to hangovers. Studies have shown that high-congener, darker-colored liquors like bourbon and whiskey lead to more severe hangovers than lighter-colored or clear liquors like vodka, which has none. A Dutch study systematically looked at the congener content and hangover risk of a variety of types of alcohol, producing the ranking above. One particular congener called methanol—found in highest levels in whiskey and red wine—has received a large amount of the blame, due to studies showing that it can linger in the body after all alcohol has been eliminated, perhaps accounting for the enduring effects of a hangover.

This, incidentally, could explain widely-held belief that mixing different sorts of liquor can cause a hangover—a greater variety of congeners could well lead to a wider variety of effects. It can't, however, explain any beliefs about the order of these drinks—despite the age-old adage "liquor-then-beer-you're-in-the-clear, beer-then-liquor-you've-never-been-sicker."

How Can You Prevent Hangovers?

The most effective solution is also the most obvious: Don't drink alcohol. Or, at the very least, don't drink to excess.

If you're set on drinking a fair amount, though, there are certain things you can do to minimize your change of a hangover and the severity of its symptoms, and they're all pretty intuitive. Don't drink quickly, on an empty stomach; drink slowly, either on a full stomach or while eating. Food doesn't literally absorb the alcohol, but having a full digestive tract slows down the rate at which your body absorbs the drug. Additionally, even though dehydration is only partly to blame, it still plays a role, so staying hydrated while drinking alcohol can help.

How Can You Quickly Cure a Hangover?

Is there a super food/drink/ritual that can magically removes the after-effects of a night spent binge drinking? Well, according to various local legends, you can cure a hangover by eating shrimp (Mexico), pickled herring (Germany), pickled plums (Japan) or drinking coffee (U.S.), strong green tea (China) or tripe soup (Romania). A number of popular foods and beverages—like the Bloody Mary, Eggs Benedict and even Coca-Cola—were even developed specifically to "cure" hangovers.

Unfortunately, there's no evidence that any of these homespun remedies do anything to help. There's also no evidence that the so-called "hair of the dog" technique (that is, drinking the morning after) has any effectiveness whatsoever. It might temporarily dull your senses, making you less aware of the hangover symptoms, but it does nothing to resolve the underlying physiological problems—and, of course, it can just lead to another hangover.

Other drinkers vouch for a variety of seemingly scientific cures—Vitamin B or caffeine, for instance—but studies have also failed to show that these provide any relief either.

So what can you actually do? You can lessen some of the symptoms with well-known over-the-counter drugs: non-steroidal anti-inflammatories, such as aspirin or ibuprofen (Advil), can treat headaches and other pain, while you can take stomach relief medicines (say, Tums or Pepto-Bismol) to reduce nausea.

You should NOT take acetaminophen (Tylenol) because when the liver is processing alcohol, it's especially susceptible to acetaminophen's toxic effects. You can eat food, drink water, and rest. It's boring, but at the moment, time is the only sure cure.

Is A Real Scientific Cure Around the Corner?

This past fall, the Web came alive with articles claiming that scientists are on the verge of developing a hangover-free beer. Unfortunately, a lot of the coverage overstated the science: So far, researchers have merely mixed electrolytes into light beer and showed that this caused less dehydration than normal beer. Because hangovers are the result of a bunch of other factors beyond dehydration, the new-fangled beer's no more of a hangover "cure" than drinking water along with your alcohol.

Other researchers, at Imperial College London, are working on synthetic blend of chemicals that produce the pleasant effects of alcohol with much lower levels of toxicity—which, in theory, could reduce the chance of a hangover. But the research is in very early stages, and given the rigorous approval process for drugs that actually treat diseases, it's easy to imagine that synthetic alcohol would take a while to get approval.