What alcohol does to your brain and body, according to the latest science

• Drinking alcohol impacts everyone a little differently.
• Musculature, water, genes, tobacco use, and other factors change an individual's risk equation.
• Here's how alcohol affects a person's body, from a first sip to potential long-term fallout.

This Dry January, the US Surgeon General is warning that the cancer risks of drinking rival smoking and obesity. A lot of this has to do with how our body processes alcohol, breaking it down into potentially cancer-causing substances along the way.

Everyone is a little different when it comes to how alcohol is managed in the body, so it's not exactly scientific to say "there is no safe level of alcohol."

Our body size, sex, muscle-to-fat ratio, how much water is in our system to dilute a drink, and certain genetic mutations all play key roles. So does the alcohol content of what we drink. A shot of vodka is more toxic to the body than a sip of beer, for example.

Given all this, developing hard and fast rules about how much alcohol is too much, and whether a little bit of alcohol is definitely harmful, is complicated.

What alcohol does to your body in the first hour of drinking

Alcohol is a tiny molecule, bathing nearly every cell in the body when we drink.

The basic trajectory of liquor in the body is from a person's mouth, through the esophagus, to the stomach, intestines, and the liver, where about 80-90% of the alcohol people consume is processed.

The liver can only process a little bit of alcohol at a time, though. How long it takes depends on how much you drink and your size, plus other factors, including how much water you have in you (muscles are more watery than fat).

As a general rule, most people will clear out one drink (like a quickly consumed shot) in two hours or less. But if a person is binge drinking, plowing through four or five drinks within a couple of hours, it's going to take about six to seven hours for the football-sized liver to metabolize that alcohol.

During that time, lots of alcohol in the "queue" is spilling out into our bloodstream, running around the body and infiltrating the brain, biding time until the liver is ready for it. This is how people get drunk.

"Once your blood alcohol level gets to a certain level, it becomes a ubiquitous substance in every part of your body," Dr. Stephen Holt, who runs the addiction recovery clinic at Yale School of Medicine, told Business Insider. "It basically goes to every organ in your body. It goes to your heart, your kidneys, your liver, of course, your brain, it's going to your bones."

About 15-30 minutes after a drink, alcohol seeping into the brain begins to change how we feel.

Inside the brain, alcohol binds to several different receptors, calming down the sympathetic nervous system, lowering stress, fear, and anxiety — helping press pause on life's worries. It also boosts feelings of euphoria, triggered by a release of dopamine, which can motivate people to seek out another drink. And finally, there's a release of beta-endorphins, our natural painkillers, for both physical and emotional woes.

The next day

The first chemical produced when our liver breaks down alcohol is acetaldehyde, a known cancer-causer.

Acetaldehyde plays a big role in hangovers: it causes nausea, which works in conjunction with the anxiety, unease, and restlessness people feel as their brain overcorrects for last night's drunken chemical imbalances.

Some folks are very efficient at turning over acetaldehyde into a vinegar-like substance (acetate) that we can pee out. Other people, including many people of Chinese, Korean, and Japanese descent, have genetic factors that slow down how fast they can process acetaldehyde, making their face flush.

It's the long-term effects of acetaldehyde on the body that scientists are most concerned about: the potential for DNA damage, chronic inflammation, liver scarring, heart disease.

People with the flushing ALDH2 gene mutation (roughly 8% of us) are at greater risk of developing issues like cancer from drinking, due to acetaldehyde's toxicity. But they're also less likely to become addicted to alcohol because they feel extra awful after they have a drink.

Over time, there's evidence that regular drinking can lead to changes in:

Head and neck:

As alcohol starts its journey down a person's throat, it can do DNA damage in oral cells.

People who smoke are able to absorb more carcinogenic chemicals in tobacco if they are drinking at the same time, as tissues become more permeable.

"A carcinogen will impact folks individually in different ways," American Cancer Society chief scientific officer Dr. William Dahut said during a recent media briefing. "There are clearly patients at higher risk for cancer, whether that's due to inherited genetic mutations, whether that's prior radiation, tobacco use."

Heart:

Controversially, there's some evidence that moderate drinking can be good for the heart, improving HDL cholesterol, and acting as a blood thinner. Federal data suggests that while roughly 178,000 Americans are killed by alcohol every year, there are about 16,000 other people across the US whose lives are saved by drinking, as they avoid more deadly heart disease, high blood pressure, and strokes.

The dose here may make the poison: heavy drinking can up a person's risk of developing irregular heartbeat issues like atrial fibrillation (AFib) and raise blood pressure, increasing the chances of a heart attack.

Breasts:

Breast cancer is responsible for most (60%) of the alcohol-related cancer deaths in women.

The risk gets stronger after a woman goes through menopause, and also increases the more she drinks. This is because drinking alcohol increases estrogen production in the body, upping the odds that cancer cells may sprout up.

The risk of developing breast cancer for a woman who drinks once per week is ~11%. But that goes up to 13% for women who have one drink a day, and 15% for women who have two.

Colon:

Irritation of the gut is probably the most important part of disease risk linked to alcohol consumption.

"It irritates the gastrointestinal lining," Aaron White, the senior scientific advisor at the National Institute on Alcohol Abuse and Alcoholism, told BI. "That sets off widespread inflammation."

Acetaldehyde and the oxidative stress from drinking also prompt DNA damage and cellular proliferation, which can lead to cancer.

Alcohol can also mess with the gut microbiome, increasing intestinal permeability, and suppressing the immune system.

Additionally, drinking alcohol can put a dent in a person's nutrition, preventing the body from absorbing folic acid, which is critical to all our cells. It can also block the uptake of important nutrients like B12 and zinc.

Liver:

Regular, heavy drinking can lead to cirrhosis, irreversible scarring and hardening of the liver.

Brain:

People often say that drinking can shrink your brain, and this is sort of true.

"By bathing all your neurons in a somewhat toxic substance, you are losing some neurons," Holt said. This can, over time, lead to early dementia.

The good news is that there is pretty solid evidence that even people who are heavy, lifetime drinkers, once they stop drinking, see much of their brain rebound in just six months, after an initial period of withdrawal.

"At any age, if you quit drinking, a lot of that damage looks like it can recover," White said. "You're not doomed."