Alcohol can increase stomach acid and delay stomach emptying. The result: nausea, vomiting and abdominal pain.

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Let’s talk about last night. Remember that decision you made to have another glass (or three) of wine? The one you’re regretting as you hug the toilet bowl with a pounding headache? As much as you’d like to wish it away, your hangover is here and it’s going to stick around for a while. Want to avoid one next time? We’ll tell you what causes a hangover, so you can prevent one in the future.

What Causes a Hangover?

The most obvious origin of a hangover is drinking too much. For some, though, even one drink can be enough to cause unpleasant symptoms. So what causes a hangover? Is it something in the alcohol that leads to the symptoms we so despise? According to Dr. Richard Stephens, BSc, Senior Lecturer in Psychology and Psychology Program Director at Keele University in the UK, a hangover can result from a variety of causes. Here are the top culprits:

• Dehydration. The first explanation for what causes a hangover, Stephens says, is dehydration. A direct result of consuming alcohol, which is a diuretic, dehydration results in symptoms such as headaches and fatigue. Drinking alcohol also increases your body’s ability to produce urine. The more you urinate, the more dehydrated you’ll get. It’s a vicious cycle.
• Low levels of glucose. Stephens also blames ketzenhammer (the German word for hangover) on a reduction in blood glucose levels. When we’re low in glucose, we often feel weak and dizzy.
• Inflammation. Another explanation for what causes a hangover, Stephens says, is the “tissue inflammation caused by the direct toxic effects of alcohol and other compounds commonly found in alcoholic beverages.” A study published in the Archives of Internal Medicine also found the severity of a hangover is related to “inflammation induced by impurities in the alcohol beverage and byproducts of alcohol metabolism.”
• Stomach irritation. Alcohol can increase stomach acid and delay stomach emptying. The result: nausea, vomiting and abdominal pain.
• Blood vessel expansion. Drinking alcohol can cause blood vessels to expand. The result: headaches.
• Poor sleep. As many of us know, alcohol can cause us to have a restless night. Drinking too much can also prevent us from getting the REM sleep necessary to feel well rested. The result: fatigue and a lessened ability to focus.  

Hangover Symptoms

Although we’re sure you’re familiar with the nasty side-effects caused by having that extra gin and tonic, here’s a list of the most common hangover symptoms:

• Diarrhea
• Difficulty focusing
• Disrupted sleep
• Dizziness
• Dry mouth
• Excessive thirst
• Fatigue
• Headache
• Increased anxiety
• Increased irritability
• Increased sensitivity to light and sound
• Lower, depressed mood
• Muscle aches
• Nausea
• Rapid heartbeat
• Shakiness
• Stomach pain
• Vomiting

Components of Alcohol That Cause a Hangover

The following ingredients are contained in alcohol. Each can have a negative impact on your body, so learning more about them can help us discover what causes a hangover. 

• Acetaldehyde. A natural product of alcohol metabolism, acetaldehyde is created during alcohol’s breakdown in the liver. It is toxic and can cause headaches and vomiting. It’s also responsible for making people blush when they’ve been drinking.  
• Ethanol. This naturally-occurring chemical compound is the main ingredient in alcohol. It is quickly absorbed by the gastrointestinal tract and then moved throughout the body.  And yes, this is the same ethanol used in gasoline. Sounds yummy, huh? Researchers from Brown University found that ethanol is also “the main source of hangover.” It causes both “subjective distress” as well as cognitive and behavioral issues.
• Congeners. These chemicals are formed during alcohol’s fermenting or distilling process and are responsible for giving alcohol it’s flavor and color. Certain drinks contain a higher level of congener than others. Dark liquors such as bourbon and brandy, for instance, have more congeners than clear liquors like vodka or gin. According to the researchers mentioned above, these high congener drinks (i.e. bourbon) result in more severe hangovers than those with little to no congeners (i.e. vodka).
• Estrogen. Certain plants used to produce alcohol contain estrogen-like substances. A study published in Alcohol Health and Research World, found “several phytoestrogens in the congeners of bourbon, beer, and wine.” Those who do not produce estrogen (i.e. postmenopausal women) experienced “estrogen-like effects” (e.g. headaches and hot flashes) even when they consumed only moderate amounts of alcohol.

Hangover Risk Factors

Some risk factors make people more susceptible to a hangover. These include:

• Ethnicity. East Asians carry a mutated gene that speeds the rate at which their livers produce acetaldehyde. That’s why they tend to flush more when they drink and experience more nausea than Caucasians.
• Drinking on an empty stomach. Turns out you really do need food in your belly before you drink. The body speeds its absorption of alcohol when there’s nothing else to digest.
• Drinking darker liquor. As mentioned earlier, darker liquor contains higher amounts of congeners, which can lead to a worsened hangover.
• Having an alcoholic in the family. Close family members who suffer from alcoholism could indicate a genetic problem that can impact your body’s ability to process alcohol.
• Smoking. Inhaling nicotine while drinking appears to increase your risk of a hangover.
• Poor sleep. It’s believed that a restless night’s sleep can worsen a hangover.

What Effects Can Hangovers Have on Our Health?

In addition to making us feel lousy and upchuck last night’s dinner, a hangover can have temporary impacts such as:

• Damage to cognitive function. According to a study published in the journal Addiction, those who participated in a heavy night of drinking suffered from impaired focus, psychomotor skills, and short- and long-term memory. They also struggled with everyday tasks such as driving.
• Disrupted sleep. A study by researchers from Brown University found that “alcohol decreased sleep efficiency and rapid eye movement sleep, and increased wake time and next-day sleepiness.”
• Slower speed. The same study found that those who are hungover have slower reaction times.

How Long Does a Hangover Last?

As much as you wish it wouldn’t, a hangover usually lasts for 18 hours after you stop drinking. “So, if you drank until midnight, your hangover would last until 6 pm the next day,” Richards explains.