The table below shows the relative risk of breast cancer for many factors. The relative risk compares the risk of breast cancer for people who have the factor to those who do not.
Factors are grouped based on the strength of the scientific evidence for each risk.
- Established and probable have the strongest evidence behind them and are recognized as linked (or not linked in some cases) to breast cancer.
- Possible factors have less evidence behind them; they suggest links to breast cancer but need more study before solid conclusions can be made.
- Insufficient or inconsistent factors are backed by few studies or the studies to date show very mixed results, which don't allow comment on any potential link with breast cancer.
Click on any of the factors to learn more.
Relative Risk Categories
Where do the data come from?
The data in this table come from two main types of research studies: observational studies (prospective cohort or case-control) and randomized controlled trials. The goal of these studies is to give information that helps support or disprove an idea about a possible link between an exposure (like alcohol use) and an outcome (like breast cancer) in people. Although they have the same goal, observational studies and randomized controlled trials differ in the way they are conducted and in the strength of the conclusions they reach.
Learn more about different types of on research studies.
Animal studies add to our understanding of how and why some factors cause cancer in people. However, there are many differences between animals and people that make it hard to translate findings directly from one to the other. And, animal studies are designed differently than human studies. They often look at exposures in larger doses and for shorter durations than are suitable for people. Thus, animal studies can lay the groundwork for research in people, but in order to draw conclusions for human populations, we need human studies.
All data presented within the Understanding Breast Cancer section of this website come from human studies unless otherwise noted.
Finding information on risk factors for breast cancer
Several organizations conduct research and/or prepare summary reports of research on certain exposures shown to have a link (or no link) to breast and other types of cancer. These agencies are a good place to find detailed, up-to-date information (for example, if you have concerns over a news item on cancer). The International Agency for Research on Cancer (IARC) is a part of the World Health Organization. The Centers for Disease Control and Prevention (CDC), the National Toxicology Program and the U.S. Food and Drug Administration (FDA) are all part of the U.S. Department of Health and Human Services.