New study highlights environmental factors that play into a woman's chance of developing cancer.
More than 200,000 women were told they have breast cancer this year, and many didn't have any well-known risk factors like taking hormone replacement therapy or carrying the breast cancer genes.
A new report is providing some answers for the women who are left wondering how this happened to them.
The report from the Institute of Medicine lists the various lifestyle factors that might be related to breast cancer, starting with those that have been proven to increase the risk for the disease.
"Those include medical radiation, the use of combined progestin and estrogen hormone therapy, the use of oral contraceptives when currently being used, as well as alcohol, and obesity and overweight," says IOM Committee Chair Dr. Irva Hertz-Picciotto.
Things that lowered the risk for breast cancer include regular physical activity and maintaining a healthy weight, especially after menopause.
Using hair dye was found not to influence the risk for the disease, as well as exposure to microwaves.
The jury is still out on several other factors like exposure to secondhand smoke, the chemical BPA and your work hours.
"Night shift work, there's growing evidence that may influence the risk for breast cancer," Dr. Hertz-Picciotto warns.
Experts agree there is still much to learn.
They hope this report will give them the clues they need to fill those knowledge gaps.
The researchers still don't know how big an impact changing your lifestyle to lower your risk for breast cancer will have, or what age is the best to start.
They say there isn't a blanket answer that helps everyone.
Women need to take their own health history into account before making any changes.