Can Smoking Cause Breast Cancer? BCRF Weighs In

Research is ongoing, but the connection between smoking and breast cancer is becoming harder to ignore. Here’s what scientists have discovered so far.

There’s a strong connection between smoking and breast cancer. Research shows that women who smoke, and even those who’ve quit, face an elevated risk of breast cancer compared with those who’ve never picked up a cigarette.

According to the Centers for Disease Control and Prevention (CDC), smoking is already a proven cause of several cancers, including those of lungs, trachea, bronchus, mouth, throat, stomach, and esophagus. But when it comes to breast cancer, scientists haven’t always been convinced of a direct link with smoking. That’s partly because breast cancer is a complex disease influenced by a wide range of risk factors, which makes it difficult to pinpoint smoking as a direct cause.

But a growing body of research makes it harder to ignore the possibility that smoking directly causes breast cancer. In fact, the Canadian Expert Panel on Tobacco Smoke and Breast Cancer Risk concluded in 2009 that “the association between active smoking and breast cancer is consistent with causality.”

In other words, evidence strongly suggests that tobacco smoke causes breast cancer, although further study is needed to fully understand how—and whether the connection also holds true for vaping, cannabis, and secondhand smoke.

Here, we unpack the latest science behind all kinds of smoking and breast cancer.

Does smoking tobacco cause breast cancer?

Scientists believe that smoking may be both a direct and indirect cause of breast cancer.

Poisons in cigarette smoke expose the breast tissue to harmful carcinogens, which can damage DNA and lead to tumor growth. In laboratory studies, rodents developed mammary tumors after being exposed to carcinogens found in cigarette smoke. Other lab studies have shown that cigarette smoke can make breast cancer cells more aggressive, helping them invade nearby tissue and spread to other parts of the body.

Toxic substances in cigarette smoke also weaken the immune system, making it harder for the body to kill cancer cells before they develop into tumors. That, combined with cigarette smoke’s ability to damage breast tissue and promote tumor growth, may help explain why women who smoke face a significantly higher risk of developing breast cancer compared with those who don’t. According to a 2011 report in The BMJ, which looked at data on nearly 80,000 women, breast cancer risk increased 16 percent in current smokers and 9 percent in former smokers compared with lifetime non-smokers.

The connection between smoking and breast cancer is even stronger among those who picked up the habit at an early age. A 2009 study published in Breast Cancer found that the risk of developing pre-menopausal breast cancer doubles for women who started smoking within five years of their first menstrual cycle. The researchers speculate that because teenage breast tissue isn’t fully developed, it may be more sensitive to the carcinogens in smoke. Overall, the more cigarettes a person smokes each day and the longer they smoke, the greater their breast cancer risk.

Scientists continue to investigate the connection between smoking and breast cancer. A 2025 presentation by researchers at the American Cancer Society found that people with cancer who smoked were more likely to develop a smoking-related secondary primary cancer, even if their first diagnosis was not directly linked to tobacco. For breast cancer survivors, current smokers were more than three times as likely to develop a second, smoking-related cancer compared with those who never smoked.

On the bright side, the risk declined significantly the longer someone had quit smoking, with a notable drop after 20 years. Committing to a smoking cessation program now—whether you’ve smoked for a few weeks or more than a decade—can make a positive impact on your overall health (including your risk of breast and other cancers).

Is secondhand smoke linked to breast cancer?

Yes, secondhand smoke has been linked to breast cancer in several studies, but further study is needed.

A 2024 comprehensive systematic review and meta-analysis in the British Journal of Cancer looked at 63 original articles on breast cancer risk in non-smoking women. The results showed that relative breast cancer risk was 24 percent higher among women exposed to secondhand smoke compared with those who weren’t. The researchers also found that it was a dose-dependent connection, meaning that the longer and more intense the exposure to secondhand smoke, the greater the breast cancer risk.

In another report, published in the International Journal of Epidemiology in 2021, researchers studied data on nearly 46,000 Norwegian women from 1991 to 2007. They discovered that those who were exposed to secondhand smoke from parents throughout their childhood were 11 percent more likely to get breast cancer than those with no smoke exposure. The scientists concluded that one in 14 breast cancer cases could have been prevented if there was no secondhand smoke exposure during childhood.

While these and other studies suggest a compelling link between secondhand smoke and breast cancer, more research is needed to determine what’s behind the connection. Breast cancer is influenced by many factors, so it’s difficult to isolate how big a role secondhand smoke (or any other individual factor) plays in the development of breast cancer. Still, the evidence is strong enough to encourage people to avoid exposing themselves or others (especially children) to secondhand smoke as a step in promoting better health and potentially lowering cancer risk.

Is vaping linked to breast cancer?

Scientists aren’t sure whether vaping causes breast cancer. The first modern e-cigarette was only invented about 20 years ago (and didn’t hit the U.S. market until the mid-2000s), so researchers don’t have the long-term data needed to fully understand its impact on breast health. But early studies suggest there could be a connection.

Vaping has been marketed as a healthier alternative to smoking, but that doesn’t mean it’s safe. The CDC notes that e-cigarettes contain carcinogens, heavy metals, and flavoring chemicals linked with lung disease. So far, it’s not clear how only vaping (and not smoking cigarettes) contributes to an individual’s risk of lung cancer, but scientists are looking for answers. A 2024 study found that people who combined vaping and cigarette smoking were four times as likely to get the disease compared with those who only used cigarettes.

Researchers have started investigating whether there may be a link between vaping and breast cancer, as well. In 2020, a report published in Cancer Letters found that breast tumors in mice grew significantly faster when the mice were exposed to vapor from e-cigarettes. Those results were echoed in a 2024 study in Frontiers in Immunology, which found that mice exposed to e-cigarettes were more susceptible to developing tumors.

And according to a 2023 study in Cancer, individuals who received a breast cancer diagnosis at a distant stage were more likely to have used e-cigarettes at some point in their lives than those who had localized breast cancer. While these studies don’t prove that vaping directly causes breast cancer, they do point to patterns that suggest a potential connection.

Is cannabis linked to breast cancer?

It’s unclear whether cannabis is linked to breast cancer. Research on the relationship between cannabis and breast cancer is limited, and the findings so far are mixed. Some suggest it could increase breast cancer risk, while others have evidence that cannabis could actually have a positive impact on breast health.

In a 2022 study published in Environmental Epigenetics, researchers looked at data on drug use and cancer rates across the United States from 2003 to 2017. They found that higher exposure to cannabis was linked with an increased incidence of breast cancer. Cannabis-friendly states also had a higher incidence of breast cancer. A 2023 study in the Journal of Cancer Research and Clinical Oncology showed similar results. It found that cannabis use may increase the likelihood of breast cancer and laryngeal cancer (and may even cause cervical cancer). The findings of these two studies don’t prove that cannabis causes breast cancer, but suggest the two are potentially linked, and more research is needed.

On the other hand, cannabis can offer breast cancer patients relief from symptoms related to their illness and treatment. A 2022 survey study on 612 breast cancer patients in Cancer found that 42 percent used cannabis to ease symptoms and treatment side effects including pain, insomnia, anxiety, nausea, and vomiting.

Scientists are also investigating the potential of cannabinoids (compounds found in cannabis including THC and CBD) to reduce breast cancer risk or to treat the disease. Researchers in a 2021 report in Molecules noted that the body’s endocannabinoid system (which regulates certain functions and can respond to certain cannabinoids) is altered in breast cancer patients. They added that estrogen receptor (ER)–negative breast cancer cells may have a sensitive response to cannabinoids, which could possibly lead to the development of new treatments involving cannabis—but there’s still a long way to go. Researchers are also studying how cannabis and cannabinoids can suppress the immune system—findings that could have implications for cancer treatments like immunotherapies.

And in 2024, a review in the Journal of Cannabis Research highlighted early lab studies showing that cannabinoids may help slow tumor growth and limit the spread of breast cancer. Still, much more research is needed before cannabis can be considered a viable treatment option or preventative measure.

The bottom line

While there’s still a lot to learn, research increasingly suggests that smoking may cause breast cancer. Vaping and cannabis may also increase the risk of the disease, although the science is still early. Even secondhand smoke has been associated with a higher risk of breast cancer, especially in individuals exposed during childhood.

Many breast cancer risk factors—like age, family history, and genetics—are outside your control. But avoiding tobacco and smoke exposure isn’t. Whether that means cutting back on vaping and cannabis, quitting cigarettes, or steering clear of secondhand smoke, finding ways to avoid tobacco and similar substances can play a positive role in your overall health, and may also decrease your cancer risk.