Smoking and Breast Cancer: What the Evidence Shows

If you are searching for smoking and breast cancer, you may be worried about your own risk, supporting someone through diagnosis, or trying to decide whether quitting still matters during treatment. The answer is more nuanced than for lung cancer. This guide sets out what major cancer organizations say, what the large studies found, how strong the evidence is for each claim, and why quitting is worth it in either case. It does not replace advice from your own care team.

Short answer: the evidence is moderate, not settled

The link is harder to pin down than for some other cancers, which is why the topic confuses people. The American Cancer Society states that “smoking tobacco increases the risk of many different types of cancer,” but that the link between smoking and breast cancer “has been difficult to study, because many people who smoke also drink alcohol, which increases breast cancer risk. Some studies suggest that smoking alone may also increase the risk of breast cancer.”

The NHS takes a practical line. Its page on the causes of breast cancer says “many breast cancers are also linked to lifestyle, such as smoking,” and its advice to lower your chance includes “try to quit smoking.”

The US Surgeon General’s 2014 report on smoking is often cited here. As summarized by the tobacco-control reference Tobacco in Australia, the report found the evidence sufficient to identify mechanisms by which smoking may cause breast cancer, but concluded: “The evidence is suggestive but not sufficient to conclude that smoking causes breast cancer.” The honest reading is that the data are consistent with a modest increase in risk, and that scientists have not proven that smoking causes breast cancer.

For the cancers that are firmly established, see our guide on what cancers does smoking cause risk data.

What the studies show about smoking and breast cancer

Two large analyses give the clearest picture. A 2015 meta-analysis in Breast Cancer Research and Treatment pooled observational studies. For ever-active smoking in 27 prospective studies, the summary relative risk was 1.10 (95% CI 1.09 to 1.12) with no heterogeneity. For current smoking it was 1.13 (1.09 to 1.17) in 27 prospective studies. The authors concluded: “There is consistent evidence for a moderate increase in the risk of breast cancer in women who smoke tobacco.”

A 2013 analysis in the Journal of the National Cancer Institute used the American Cancer Society’s Cancer Prevention Study II Nutrition Cohort, with 73,388 women and 3,721 invasive breast cancers over a median 13.8 years. Incidence was higher in current smokers (hazard ratio 1.24, 95% CI 1.07 to 1.42) and former smokers (1.13, 1.06 to 1.21) than in never smokers. When the authors combined their results with 14 other cohort studies, the association was weak: 1.12 (1.08 to 1.16) for current smoking and 1.09 (1.04 to 1.15) for former smoking.

These are modest increases, in the range of 10 to 20 percent, and they come from observational studies, so they cannot prove cause. Alcohol is the obvious complication: the 2013 paper found that alcohol did not confound the associations with smoking status, but that neither current nor former smoking was associated with risk among never drinkers (P for interaction = .11). That is one reason the American Cancer Society calls the question hard to study. If you drink as well as smoke, our smoking and cancer statistics article puts these risks in a wider frame, and the American Cancer Society also notes that “no amount of alcohol is completely safe.”

Does starting young matter more?

This is where the signal appears strongest. In the 2013 analysis, women who started smoking before menarche had a hazard ratio of 1.61 (95% CI 1.10 to 2.34), and those who started after menarche but 11 or more years before their first birth had 1.45 (1.21 to 1.74). In the pooled meta-analysis, women who started before their first birth had a hazard ratio of 1.21 (1.14 to 1.28). The authors concluded that the results “support the hypothesis that active smoking is associated with increased breast cancer risk for women who initiate smoking before first birth and suggest that smoking might play a role in breast cancer initiation.”

The wording matters: “associated” and “might.” It is a hypothesis supported by cohort data, not a proven mechanism. Whatever your start age, you cannot go back, but you can stop adding years of exposure, and in the pooled analysis former smokers had a somewhat lower relative risk than current smokers (1.09 versus 1.12).

Secondhand smoke

The same 2015 meta-analysis looked at passive smoking. For ever passive smoking in 11 prospective studies, the summary relative risk was 1.07 (95% CI 1.02 to 1.13) with little heterogeneity. In 20 retrospective studies it was 1.30 (1.10 to 1.54), but with high heterogeneity, which means those studies disagreed with each other and the figure is less reliable. The authors wrote that “the evidence for a moderate increase in risk with passive smoking is more substantial than a few years ago.”

In practical terms, if you live with a smoker, your own risk is not zero but the effect is small compared with the benefits of a smoke-free home. A smoke-free home is also a gift to everyone else in it, which makes a household quit worth planning together.

Smoking during breast cancer treatment

For people who already have breast cancer, the picture is clearer, and more urgent. A 2020 systematic review of smoking and adjuvant breast radiotherapy included 71 articles and 198 outcomes in seven categories, including skin reactions, cardiovascular effects, reconstruction outcomes, lung function, mortality and recurrence. Between 29 and 71 percent of the outcomes in each category showed significant differences between smokers and non-smokers, depending on the category, and “none of the articles reported non-smokers to have a higher risk than smokers.” The authors concluded that smoking “can pose a higher risk of post-treatment complications that can influence an individual’s quality of life, survival rate and/or recurrence risk.”

This National Cancer Institute video looks at why smoking matters for people having cancer treatment.

Surgery and reconstruction are where timing can be concrete. In a 2000 study of free TRAM flap breast reconstruction (936 reconstructions in 718 patients), smokers had a higher incidence of mastectomy skin flap necrosis than non-smokers (18.9 percent versus 9.0 percent). The authors reported that “smoking-related complications were significantly reduced when the reconstruction was delayed or when the patient stopped smoking at least 4 weeks before surgery.” A smaller 2017 study of nipple-sparing mastectomy at one center found equivalent reconstructive outcomes between people with and without a smoking history, with signs of higher risk of complete nipple-areola necrosis for a history above 10 pack-years or fewer than 5 years since quitting. Your surgeon will have their own rules, so ask what applies to your operation.

Survival and quitting after a diagnosis

A 2014 study and meta-analysis in Breast Cancer Research examined 5,892 women treated in one Canadian center. Current smokers at diagnosis had a slightly but not statistically significant higher breast cancer-specific mortality (hazard ratio 1.15, 95% CI 0.97 to 1.37). Combined with published studies, the meta-analysis found a statistically significant 33 percent higher mortality from breast cancer in smokers at diagnosis (hazard ratio 1.33, 1.12 to 1.58), and the authors concluded that smoking at diagnosis “is associated with a reduction of both overall and breast cancer-specific survival.”

A 2016 study in the Journal of Clinical Oncology followed 20,691 women with localized or regional invasive breast cancer and 2,894 breast cancer deaths. Active smokers one year before diagnosis were more likely than never smokers to die of breast cancer (hazard ratio 1.25, 1.13 to 1.37), and the 10 percent who continued to smoke after diagnosis had a hazard ratio of 1.72 (1.13 to 2.60). When compared with women who kept smoking, those who quit after diagnosis had lower mortality from breast cancer (0.67), but the confidence interval (0.38 to 1.19) was wide enough that the result was not statistically significant. The same group had a lower risk of death from respiratory cancer (0.39, 0.16 to 0.95), which was statistically significant.

So the fair summary is this. Smoking before or after diagnosis is associated with higher mortality. Quitting after diagnosis was associated with significantly lower respiratory cancer mortality and with lower, but not statistically significant, breast cancer mortality in that study. Quitting still clearly protects against the other smoking-related diseases that cancer patients face. We cover the wider topic in quitting smoking after a cancer diagnosis. If you are a woman wondering why stopping can feel so hard, see is it harder for women to quit smoking, and for another cancer where the link with smoking is firmer, read smoking and cervical cancer risk.

How to quit around a diagnosis or worry

• Tell your oncology or breast care team. Quitting support is part of care at many cancer centers; ask what is offered.
• Ask about timing. If you are facing surgery or reconstruction, ask how long before the procedure they want you smoke-free.
• Do not wait for a perfect moment. Treatment is stressful, but the studies above suggest stopping is worthwhile at any stage.
• Use more than one kind of help. Counseling, medicines and a tracking tool often work together; see our what happens when you quit smoking complete health recovery guide.
• Reduce alcohol too. The American Cancer Society says it is best not to drink alcohol, and if you do, women should have no more than 1 a day.

The free iQuit app can support the quitting side. You can choose cold turkey or gradual reduction, log cravings and their triggers, use SOS tools when an urge hits, and track smoke-free days and money saved. It does not screen for, diagnose or treat breast cancer, so it works alongside your care team and never replaces mammograms or treatment. You can see how it compares in our best quit smoking apps feature comparison rankings.

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