If you watch the news or check the latest posts on social media, it seems like more and more people are sharing stories about a friend, coworker or family member being diagnosed with cancer at a young age. These stories leave many people wondering, is cancer really becoming more common in younger adults? 

The short answer to this question is, yes. For some types of cancer, including breast cancer, researchers are seeing an increase among younger adults. And while scientists don’t have a clear explanation for this yet, they’re currently working to understand why it’s happening and how it could impact prevention and early detection. 

What the Numbers Say 

Right now, breast cancer is still much more common in women over age 40, and only about 4% of all breast cancers diagnosed in the U.S. occur in women under 40. However, diagnoses among younger women have been gradually increasing. 

According to the American Cancer Society, overall, the incidence of breast cancer among women in the U.S. increased by 1% annually from 2019 to 2023 (most recent data available), with a steeper increase among women younger than age 50 (nearly 2% per year) than in those who were 50 or older (0.7%) per year. While these increases in rates for young women are modest from year to year, they add up over time and have caught the attention of researchers around the world. 

It is important to note that most young women will not develop breast cancer. 

But understanding why breast cancer rates are increasing may help scientists identify ways to reduce risk in the future. 

Why Is This Happening? 

So, what’s behind the rise in breast cancer in young women? The truth is no one knows for sure. Researchers believe it’s probably not due to one single cause, but a mix of lifestyle, environmental and biological factors. Many of these potential contributors are still being studied today. 

Lifestyle Factors 

Through clinical trials, researchers are exploring whether changes in modern lifestyles may play a role in breast cancer, including an increase in body weight, decline in childbirths, lower levels of physical activity, alcohol consumption and smoking or tobacco exposure. These factors have long been associated with overall health and, in some cases, breast cancer risk. However, they still do not fully explain why diagnoses are increasing among younger adults. 

Environmental Exposure 

Scientists are also investigating whether exposure to certain chemicals in everyday life could influence cancer risks for young adults. Researchers are studying chemicals found in some plastics, certain cosmetics and personal care products, industrial pollutants and environmental contaminants. 

Some of these chemicals are known as endocrine-disrupting chemicals, meaning they can interfere with normal hormone function. Researchers are investigating whether long-term exposure to these chemicals could contribute to breast cancer risk, but to date, no environmental toxins related to breast cancer have been found. More research is needed before any conclusions can be made. 

Biological Factors 

One of the most active areas of breast cancer research involves the study of hormones. Breast cells are influenced by the hormones estrogen and progesterone. Research has shown that the longer breast tissue is exposed to these hormones over a person’s lifetime, the greater the risk becomes of developing breast cancer. 

One way that scientists can measure this exposure to hormones is by looking at the total number of menstrual cycles a woman has. Over the past few decades, this number has increased for many women because girls are beginning puberty at younger ages, and many women are entering menopause later in life. Today, women are also having fewer pregnancies, with some having their first child later in life or not having children at all. Each of these factors can increase a woman’s lifetime exposure to estrogen and progesterone and possibly increase their risk of developing breast cancer. 

What Does This Mean for You? 

If you are a young woman, it’s natural to be concerned about these trends. While breast cancer remains relatively uncommon for most young women, these findings highlight the importance of paying attention to your health, discussing any concerns you have with your doctor and when to start breast cancer screening. 

Knowing your risk can start with talking to both sides of your family so that you know your family history. If it is helpful, genetic counseling and testing can also help determine whether you carry any hereditary risk factors. 

Beyond your personal biology, get to know what “normal” looks like for you and let your doctor know if you notice any changes. You should be receiving a clinical breast exam at least every three years starting at age 25, and if you are at average risk, start getting your annual mammogram at age 40. If you are at higher risk, speak with your doctor about what screening tests are right for you and when to start screening. 

While no lifestyle change can eliminate breast cancer risk, being physically active, maintaining a healthy weight, limiting alcohol and not smoking are linked to a lower risk of breast cancer. 

Researchers continue to explore why more young adults are developing cancer. As new research discoveries emerge, they may lead to better prevention strategies, earlier detection and more personalized ways to identify those at higher risk. Today, many questions remain, but understanding why these cancers are on the rise is an important step toward protecting the health of future generations. 

Learn more about breast cancer risk factors. 

Explore Komen’s Breast Self-Awareness guide. 

For more information, visit komen.org or call the Komen Patient Care Center’s Breast Care Helpline at 1-877 GO KOMEN (1-877-465-6636) Monday through Thursday, 9 a.m. to 7 p.m. ET and Friday, 9 a.m. to 6 p.m. ET or email at helpline@komen.org. Se habla español.