The Centers for Disease Control and Prevention has been clear about the risk factors for breast cancer. They include:

• Late or no pregnancy: Having the first pregnancy after age 30 and never having a full-term pregnancy raises breast cancer risk.
• Inactivity: Women who are not physically active have a higher risk of getting breast cancer.
• Getting older: Most breast cancers are diagnosed after age 50.
• Having dense breasts: Dense breasts have more connective tissue than fatty tissue, which can sometimes make it hard to see tumors on a mammogram.
• Drinking alcohol.
• Family history of breast cancer: A woman’s risk for breast cancer is higher if she has a mother, sister, or daughter or multiple family members on either her mother’s or father’s side of the family who have had breast cancer. Having a first-degree male relative with breast cancer also raises a woman’s risk.
• Taking certain oral contraceptives.

• Early menstrual period: Women who start their periods before age 12 are exposed to hormones longer, thereby raising their risk for breast cancer.
• Starting menopause after age 55.
• Being overweight or obese after menopause.
• Previous treatment using radiation therapy: Women who had radiation therapy to the chest or breasts before age 30 have a higher risk of getting breast cancer later in life.
• Genetic mutations: Inherited mutations to certain genes, such as BRCA1 and BRCA2.

To these “traditional” breast cancer risk factors, researcher Sanna Heikkinen from the University of Helsinki and Finnish Cancer Registry would add two more: the use of hormonal contraceptives and hair dyes.

Hikkinen's research included self-reported survey data from 8,000 breast cancer patients and 20,000 controls from Finland. The results show that use of a hormonal intrauterine device was associated with a 52 percent increased risk of breast cancer in post-menopausal women, when contrasted with women who had used copper intrauterine device.

Use of other hormonal contraceptives was associated with a 32 percent higher breast cancer risk among younger women under 50 when compared to women who did not use hormonal contraceptives.

Hikkinen also observed a 23 percent increase in the risk of breast cancer among women who dyed their hair compared to those who did not.

To confirm the roles of these factors, Hikkinen cautions that further research on the effects of hormonal contraceptives, most specifically hormonal intrauterine devices and hair dyes, is needed with other populations.

The research has been published by the University of Helsinki.