No one knows for certain what causes breast cancer. However, a number of risk factors are known to increase the chance of developing breast cancer - but these does not necessarily mean that a person will get the disease.
There are different kinds of risk factors. Some of these factors are beyond control, while some are linked to cancer-causing factors in the environment or due to lifestyle and personal choices such as pregnancy, smoking, and drinking.
Risk factors that you cannot change
Risk factors that are lifestyle related
Risk factors with uncertain, controversial or unproven effect