There are several risk factors that increase the likelihood of developing breast cancer. Having these risk factors does not mean a person will definitely develop breast cancer, just that they may have a higher chance of one day developing it.

There are two main categories of risk factors for breast cancer — ones a person can change and ones they cannot change.

There are also potential risk factors that researchers, scientists, and doctors are currently examining. However, more research is necessary to determine if these factors definitely increase the risk of developing breast cancer.

This article reviews known risk factors, both changeable and unchangeable. It also explores emerging risk factors, things that place people at a high risk of developing breast cancer, and ways to lower the risk.

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According to the Centers for Disease Control and Prevention (CDC), some common risk factors for breast cancer that a person cannot change include:

  • Having dense breasts: Those with dense breasts are more likely to develop breast cancer. Additionally, as dense breasts have more connective tissue compared with fatty tissue, it can be more difficult to see tumors on a mammogram.
  • Genetic mutations: Inherited gene changes, including the BRCA1 and BRCA2 mutations, can increase the risk of breast cancer and ovarian cancer.
  • Reproductive history: Starting menstruation before age 12 and reaching menopause after age 55 both increase a person’s exposure to certain hormones, resulting in an increased risk of breast cancer.
  • Increased age: The risk of breast cancer appears to increase with age. More people over the age of 50 receive a diagnosis of breast cancer.
  • A family history of breast cancer: A person has an increased risk of breast cancer if any first degree relatives such as a sister or mother or multiple relatives from either side of the family have experienced breast cancer. The risk is also increased if a first degree male relative has had breast cancer.
  • Exposure to medication diethylstilbestrol (DES): DES was a type of medication that doctors gave to pregnant people to help prevent pregnancy loss between 1940 and 1971. Those who took the medication or had a birth parent who took it are at increased risk of developing breast cancer.
  • Exposure to radiation treatment for another cancer: Those who underwent radiation therapy before the age of 30 have an increased risk of developing breast cancer.
  • A personal history of breast cancer or other breast conditions: A person’s risk increases if they have experienced breast cancer before. It also increases if a person has experienced noncancerous conditions that affect the breast such as atypical hyperplasia, which is an accumulation of abnormal cells in breast ducts or lobules.

While a person cannot change their medical history or genetics, they can make changes to affect the following common risk factors for breast cancer:

Hormones and breast cancer risk

A person’s risk of developing breast cancer has an association with exposure to estrogen and progesterone, hormones the ovaries produce. Exposure to these hormones at high levels or for a long time can increase breast cancer risk.

As a result, taking hormones in the form of hormone replacement therapy for menopause for longer than 5 years can increase a person’s risk of developing breast cancer, as can taking oral contraceptives.

Aspects of a person’s reproductive history can also increase their breast cancer risk, including:

  • being pregnant for the first time after the age of 30
  • not breastfeeding
  • never having had a full-term pregnancy states that during adolescence and until a person has a first full-term pregnancy — if they choose to do so — the breast cells are immature and very active. Adolescent breast cells also respond to estrogen and other chemicals that disrupt hormones. The main reason a full-term pregnancy can reduce the risk of breast cancer is that during pregnancy, the cells mature and grow.

Additionally, experiencing pregnancy can lower the total number of menstrual cycles a person has in their lifetime, reducing their exposure to estrogen.

According to Cancer Research UK, it is unclear why breastfeeding or chestfeeding lowers a person’s risk of developing breast cancer. However, it states that medical professionals theorize it may be because the ovaries do not produce eggs as often if a person breastfeeds, or because breast cells change during breastfeeding. This may make them more resistant to the changes that lead to breast cancer.

Emerging risk factors are those that are new and not well-studied. In other words, they may one day become known risk factors, but require additional studies to prove their safety or danger.

Some potential risk factors include:

  • An unhealthy diet: Having obesity and overweight are risk factors for breast cancer. If possible, a person should aim to eat a diet that consists of fruits, vegetables, whole grains, and legumes to provide the body with the nutrients it needs.
  • Exposure to chemicals in water: This may be a result of incorrect disposal of medications, cleaners, and other substances. People may wish to drink filtered water from the faucet as bottled water is not as well regulated.
  • Low vitamin D Levels: Low vitamin D levels may have an association with an increased risk of breast cancer. Vitamin D plays a role in the growth of healthy breast cells. However, more research is necessary to confirm these findings.
  • Exposure to chemicals in plastic: Chemicals such as bisphenol A may increase the risk of cancer.
  • Exposure to chemicals in grilled or prepared food: Foods that people cook at a high temperature until they are well-done can form chemicals called heterocyclic animes. These may increase the risk of cancer.

According to the CDC, people with an inherited mutation to their BRCA1 and BRCA2 genes and those with a strong family history of breast cancer have a higher risk of developing breast cancer.

People in these categories may wish to speak with a doctor about ways to reduce their risk.

Learn more about the BRCA genes.

People can take several steps to minimize their risk of developing breast cancer or increase the likelihood of catching it at an earlier stage, such as by:

  • starting mammogram testing in their 40s if they have a family history of the condition
  • following exercise recommendations by doing a minimum of 150 minutes of medium intensity cardio workouts or activities a week
  • achieving and maintaining a moderate weight
  • avoiding alcohol or limiting their intake

A person may also find that avoiding smoking and eating a healthy diet help.

For more resources on breast cancer management and treatment, visit our dedicated hub.

Breast cancer has several known risk factors. A person cannot control some factors, such as age and genes. Risk factors a person can control include alcohol consumption and smoking.

People may wish to take steps to reduce their overall risk, such as by eating a healthy diet, exercising, and avoiding or limiting alcohol consumption.