“Alcohol is a well-established, preventable cause of cancer responsible for about 100,000 cases of cancer and 20,000 cancer deaths annually in the United States—greater than the 13,500 alcohol-associated traffic crash fatalities per year in the U.S.—yet the majority of Americans are unaware of this risk,” Murthy said in a Jan. 3 news release accompanying the report Surgeon General’s Advisory on Alcohol and Cancer Risk. “This Advisory lays out steps we can all take to increase awareness of alcohol’s cancer risk and minimize harm.”

Among the report’s most sobering facts is that you don’t have to partake in binge drinking or have alcohol use disorder to put yourself at risk. Consuming a single daily drink is enough. In 2020, more than 741,000 cancer cases worldwide were attributable to alcohol consumption. However, the percentage of cases among people who consumed two or fewer drinks per day (25%) was comparable to that of those who had six or more drinks a day (26%).

“The risk of cancer is lower at lower levels of consumption,” the report reads. “However, many more people consume [two or fewer] drinks per day, thus leading to a similar number of overall cancer cases at lower levels as higher levels of consumption.”

So how, exactly, does alcohol cause cancer? The surgeon general’s advisory highlights the following four ways.

1. Your body converts alcohol into a toxic chemical

Everything you eat or drink gets broken down into its elemental components, explains Dr. Mikkael Sekeres, chief of hematology at the University of Miami Sylvester Comprehensive Cancer Center. That’s how your body determines which nutrients to absorb and what to get rid of.

When you consume an alcoholic beverage, your body metabolizes the ethanol into a toxic chemical called acetaldehyde, which is capable of damaging your DNA.

“Cancer is a cell that has abnormal growth, and it’s lost the ability to listen to the body’s signals to stop growing,” Sekeres tells Fortune. “What causes that abnormal growth is damage to DNA as the cell is dividing, and it creates a cell with damaged DNA that has a growth advantage compared to other cells around it.”

Sekeres continues, “Acetaldehyde is the link between alcohol and DNA damage—at least the cells that can grow uncontrollably, which is the definition of cancer.”

2. Alcohol increases inflammation

You may be familiar with the term “antioxidant” as a wellness buzzword, and know that foods rich in antioxidants, such as beets and blueberries, may improve your health. Alcohol generates unstable molecules called reactive oxygen species. Also known as oxygen radicals, they can ruin DNA, RNA, and proteins in addition to causing cell death. Antioxidants, as the name suggests, can protect cells from such oxidative stress.

“Another way of thinking about what can lead to cancer,” Sekeres says, “is anything that causes our cells to grow over and over and over again increases the likelihood, statistically, that during one of those cycles of growth, they’re going to make a mistake.”

Oxidative stress does just that—induces inflammation, which in turn prompts high cell turnover.

3. Alcohol spikes estrogen, upping breast cancer odds

Drinking alcohol upsets your hormone levels. Most notably, alcohol’s influence on sex hormone estrogen is tied to breast cancer, explains Dr. Douglas Marks, a breast oncologist at NYU Langone Health.

“Alcohol can raise the estrogen levels in the body, primarily by its effect on the liver,” Marks tells Fortune. “Where the liver should usually metabolize estrogen, that rate of estrogen breakdown could be reduced and, as a result, estrogen levels can be higher.”

What’s more, alcohol can increase production of estrogen, which stimulates breast tissue and can lead to certain types of breast cancer, Marks says.

4. Alcohol helps you absorb other carcinogens, especially tobacco

Where there’s smoke, there’s fire. Using a similar logic, where people are drinking alcohol, there may also be people smoking tobacco, a notorious carcinogen. Because tobacco smoke particles can dissolve in alcohol, drinking such a contaminated substance can up your odds of developing mouth and throat cancers.

“I would propose another mechanism,” Sekeres says. “I bet that there are a lot of people who like to smoke a cigarette while they’re drinking their beer or having their whiskey or drinking their wine. So it may be that the behavior is associated with another high-risk behavior: smoking that can also lead to cancer.”

Read more from Fortune

Is there a safe amount of alcohol to drink?

The surgeon general’s report highlights the link between alcohol and at least seven types of cancer: 

• Breast (in women)
• Colon and rectum
• Esophagus
• Liver
• Mouth (oral cavity)
• Throat (pharynx)
• Voice box (larynx)

“Daily consumption of alcohol increases the risk of these seven major cancer types, including breast cancer, and that consumption doesn’t need to be very much,” Marks says. “For individual patients, special-occasion drinking or drinking intermittently likely has very little impact on their cancer risk.

“Whereas routine drinking does carry increased risk—particularly greater than two drinks per day, but also we’re seeing this increase in even daily drinking of one drink or more per day.”

Because the association between alcohol and cancer is so clear, Sekeres says, people might consider taking a hard look at their drinking habits and overall health.

“Each of us has to make a decision about the amount of risk we are willing to accept in participating in a behavior that we find pleasurable,” Sekeres says.

If you or a loved one are struggling with alcohol use, the National Institute on Alcohol Abuse and Alcoholism (NIAAA) Alcohol Treatment Navigator can connect you to self-guided programs, telehealth treatment, mutual support groups, and health care professionals who are trained to help. If you need immediate support, contact the 988 Suicide & Crisis Lifeline.

For more on how alcohol impacts your health:

• Just one alcoholic drink a day can increase your risk of cancer. But most Americans don’t know the dangers, new survey says
• Alcohol has a clear link to at least 7 types of cancer. Now the Surgeon General wants updated warning labels on booze
• Alcohol-fueled hospital visits are spiking among middle-aged women, study says: ‘We simply just don’t know what’s causing this’
• Binge drinking is on the rise among older adults. Here’s why it’s more dangerous and how to spot the signs
• Is moderate drinking good for your health? Science says no