Causes of Breast Cancer

What actually causes breast cancer? 

These DNA changes can be inherited (present from birth) or acquired during a person’s lifetime. Most are acquired rather than inherited, meaning most breast cancers are not caused by an inherited gene mutation. While every breast cancer begins with damage to a cell’s DNA, that doesn’t always explain why those DNA changes happened in one person and not another.

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Why you usually cannot pinpoint one cause

One of the first questions many people ask after a breast cancer diagnosis is, “Why did this happen to me?” It’s a completely understandable question, but for most people, there isn’t one clear answer. 

Breast cancer is usually the result of many factors working together over time rather than one specific event, exposure, or choice. Researchers have identified risk factors that can increase or decrease the chance of developing breast cancer, but having one, or even several, risk factors does not mean they caused your breast cancer. 

Likewise, many people—approximately 70%—who develop breast cancer have few or even no known risk factors outside of age and being female. Only approximately 10% of people with a known family history are diagnosed. Risk factors help us understand who may be more likely to develop breast cancer, but they usually can’t explain exactly why one person develops it, and another does not.

A risk factor is not the same as a cause

Knowing the difference between a risk factor and a cause can help make sense of why breast cancer develops in some people but not others. 

A breast cancer risk factor is anything that increases the chance of developing a disease; it is not the cause of the disease. Instead, risk factors increase the chance that DNA damage may occur in breast cells over time. Having one or even several risk factors does not mean you will develop breast cancer. In fact, many people with risk factors never get breast cancer, while others who are diagnosed have few or no known risk factors at all.

There are many factors that can influence a person’s chance of developing breast cancer. Some risk factors cannot be changed, while others are related to lifestyle factors that may influence breast cancer risk over time. 

Risk factors you cannot change

Risk factors you cannot change include your genetic makeup, ancestry, and personal health history. These factors include:

• Gender: Women are nearly 100 times more likely to develop breast cancer than men
• Age: Most breast cancers are diagnosed in women aged 55 and older
• Family history: Having a first-degree relative (parent, sibling, or child) or multiple second-degree relatives (grandparent, aunt, uncle, niece, or grandchild) with breast cancer
• Inherited gene mutations: Inheriting a mutation in a gene associated with breast cancer, such as BRCA1 or BRCA2
• Dense breast tissue: Dense breast tissue increases the risk of diagnosis.
• Ashkenazi Jewish ancestry: People of Ashkenazi Jewish heritage are more likely to carry inherited BRCA1 or BRCA2 gene mutations
• Personal history of breast cancer or certain breast changes: A personal history of breast cancer or high-risk breast changes, such as atypical ductal hyperplasia (ADH), atypical lobular hyperplasia (ALH), or lobular carcinoma in situ (LCIS)
• Radiation therapy to the chest at a young age: Receiving radiation therapy to the chest before age 30, such as for Hodgkin lymphoma
• Personal or family history of ovarian cancer: A personal or family history of ovarian cancer
• Early menstruation: Starting your menstrual periods before age 12
• Later menopause: Going through menopause after age 55
• Never having given birth: Never having given birth (nulliparity) is associated with a slightly higher risk

Rick factor you may be able to influence

• Alcohol: Drinking alcohol increases breast cancer risk, and the risk begins to rise even at low levels of alcohol consumption. In 2025, the U.S. Surgeon General identified alcohol as a leading preventable cause of cancer and noted that breast cancer risk can increase with around one drink per day or less.
• Smoking: Smoking increases the risk of breast and other types of cancer
• Physical activity: Regular physical activity has been shown to lower risk
• Body weight: Maintaining a healthy body weight, especially after menopause
• Breastfeeding: Breastfeeding may slightly lower risk, particularly when breastfeeding for a longer period of time
• Hormone replacement therapy (HRT): Some types of hormone replacement therapy (HRT) may slightly increase the risk of breast cancer, depending on the type of hormones used and how long they are taken. Talk with your healthcare provider about the benefits and risks based on your personal health history.

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What does not cause breast cancer

There are many myths about what causes breast cancer, and it can be difficult to sort through the overwhelming amount of information online. While some claims can sound convincing, current scientific evidence does not support many of these concerns.

The following things do not cause breast cancer:

Antiperspirants and deodorants

Although the terms are often used interchangeably, deodorants help control body odor, while antiperspirants reduce sweating. There is no evidence that using either product increases the risk of breast cancer. Some antiperspirants contain aluminum, which can occasionally show up on a mammogram. Some imaging centers recommend avoiding these products on the day of your mammogram to improve image quality, not to reduce your risk. 

Bras and underwire

There is no evidence that wearing a bra, including a bra with underwire, increases the risk of breast cancer. Research, including a large population-based study, has shown no credible link between bra-wearing habits, including the length of time a bra is worn or underwire use.

Abortion and miscarriage

According to the National Cancer Institute, research has shown that abortion or miscarriage does not increase a woman’s risk of breast cancer. Earlier studies raised questions about a possible link, but those studies had important limitations. Since then, larger, better-designed studies have consistently found no evidence that abortion or miscarriage increases breast cancer risk.

Carrying a cell phone in your bra

The National Cancer Institute states that there is no evidence that carrying a cell phone in your bra increases the risk of breast cancer. Unlike X-rays, which use high-energy radiation that can damage DNA, cell phones use low-energy radiofrequency waves. Although researchers continue to study the long-term health effects of cell phones, current research has not found a link between carrying a cell phone in your bra and developing breast cancer. 

Breast implants

Breast implants do not increase the risk of breast cancer. However, implants can make it more difficult to see all of the breast tissue on a mammogram. To improve the exam, the mammography technologist will usually take additional images called implant-displaced (Eklund) views, which help visualize more breast tissue. Be sure to let your mammography technologist know if you have breast implants before your exam, so the appropriate images can be obtained. 

Although breast implants do not increase the risk of breast cancer, the  U.S. Food and Drug Administration (FDA) has identified a rare type of non-Hodgkin lymphoma called breast implant-associated anaplastic large cell lymphoma (BIA-ALCL) that can develop in the scar tissue and fluid surrounding a breast implant. BIA-ALCL is not breast cancer, and most cases are successfully treated with surgery when diagnosed early.

Other things that do not cause breast cancer

A few other common concerns below are often linked to breast cancer, but current research has not found evidence that they directly cause harm.

• Caffeine: Drinking coffee, soda, energy drinks, or other caffeinated beverages does not cause breast cancer.
• Microwaves: Using a microwave or eating microwaved food does not cause breast cancer.
• Contact with someone who has cancer: Breast cancer is not contagious and cannot be spread through touching, hugging, kissing, or sharing food with someone who has it.
• Stress: Stress has not been shown to directly cause breast cancer. However, managing stress is still important for your overall health and well-being.

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“Did I cause my breast cancer?”

After being diagnosed with breast cancer, many women may ask themselves if they did something to cause their cancer. It’s a completely understandable concern, but breast cancer is often not caused by something you did.

Breast cancer is not caused by one meal, one product, one stressful time in your life, or one decision you made years ago. It is not a punishment or consequence for something you did or didn’t do. Most breast cancers develop because of a combination of factors, many of which cannot be controlled or fully explained.

Although some lifestyle habits can influence breast cancer risk, they cannot tell us who will or will not develop the disease. Many people with known risk factors never develop breast cancer, while others with few or no known risk factors do.

If you’ve been diagnosed with breast cancer, it’s natural to wonder why it happened. But in most cases, there simply isn’t one thing that caused it.

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Can breast cancer be prevented?

Breast cancer usually cannot be fully prevented, and there is no guaranteed way to avoid developing it. Healthy habits, such as limiting alcohol, staying physically active, eating a balanced diet that emphasizes fruits, vegetables, whole grains, legumes, and lean sources of protein, and maintaining a healthy weight after menopause may help lower your risk, but they alone cannot prevent breast cancer. The most important thing you can do is to find breast cancer early, when treatment is often more effective and outcomes are generally better.

For some people, however, there are options that can greatly reduce the risk of developing breast cancer. People with certain inherited gene mutations or those at very high risk because of their personal or family history may choose to have a risk-reducing mastectomy (also called a preventive or prophylactic mastectomy), which can lower the risk of breast cancer by up to 98%. 

Others may be candidates for hormone-reducing medications, such as tamoxifen, raloxifene, or aromatase inhibitors. When taken as recommended, these medications can lower the lifetime risk of developing hormone receptor-positive breast cancer usually by half. 

Knowing your risk for breast cancer is an important step in determining what factors—if any—you should be mindful of and try to influence. Begin by talking to your doctor about taking a breast cancer risk assessment, such as the Tyrer-Cuzick, to determine your risk and any next steps to protect your breast and overall health.

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Sources

National Cancer Institute
American Cancer Society
American Cancer Society

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