Just this month, two young, high-profile public figures announced that they have cancer. First, Olivia Munn, 43, disclosed that she was treated for breast cancer after catching it early. Days later, Kate Middleton, 42, announced she has been receiving treatment for an unspecified form of cancer.

Their diagnoses spotlight a troubling trend: both in the U.S. and around the world, cancer diagnoses are growing more common among adults younger than 50. By 2030, one recent study estimated, the number of these early-onset cancer diagnoses could increase by roughly 30% worldwide—and the number of people who die from their conditions could rise by about 20%.

“The most striking finding in the last decade has been this rise in incidence rates among young adults,” says Ahmedin Jemal, senior vice president of surveillance and health equity science at the American Cancer Society (ACS).

Cancer is still most commonly diagnosed among people older than 65. In the U.S., only about 12% of cancers are diagnosed among adults younger than 50, according to ACS data. A woman in the U.S. has about a one in 17 chance of being diagnosed before she turns 50, while a man has about a one in 29 chance, the ACS says. (Women are more likely to be diagnosed largely because breast cancer is so common.)

But those odds are gradually getting worse. In 2019, about 103 cancers were diagnosed among every 100,000 U.S. adults younger than 50, up from about 100 in 2010, according to a 2023 study in JAMA Network Open. That may seem like a small overall increase, but it’s not a good sign—especially since, during the same period of time, incidence rates among older U.S. adults decreased. “It’s almost like the curves have reversed themselves,” says Dr. Richard Barakat, director of cancer care at Northwell Health in New York.

For certain types of cancer, the numbers are especially striking. Colorectal cancer is now diagnosed among young adults almost twice as often as it was in the 1990s, according to one 2022 study, and the JAMA Network Open researchers found that other types of gastrointestinal cancer are also on the rise among this population. Early-onset breast cancer is becoming more common too, with its incidence rising by almost 4% among U.S. women every year from 2016 to 2019, according to a 2024 study. Even lung cancer, a disease typically associated with older cigarette smokers, is now to a surprising degree affecting younger women, even those who have never smoked, says Dr. Matthew Triplette, a pulmonologist at Fred Hutch Cancer Center in Seattle.

What’s driving these trends? Triplette says he doubts there’s “some new, very dangerous cancer risk factor out there that’s causing tons of excessive cases in younger folks.” Cancer is a complex disease influenced by a mixture of genetics, lifestyle choices, and environmental exposures, so it’s unlikely that there’s a single explanation for the data.

Instead, it’s likely a mix of things. Eating lots of processed foods, not getting enough exercise, and drinking too much alcohol are all risk factors for cancer, and all of those issues are widespread in modern life. A 2019 study co-authored by Jemal found that many of the cancers growing more common among U.S. young adults are linked to obesity, which now affects about 40% of U.S. adults under 40.

Researchers are also studying the gut microbiome’s role in cancer development. Everything from what you eat to the medications you take can affect the health of your gut microbiome, Barakat says, so it’s feasible that aspects of the modern diet—or the medical system’s over-reliance on antibiotics—could have trickle-down effects. Exposure to pollutants in the environment could play a role, too, Triplette says.

Even big societal changes could have an impact, Jemal says. For example, research shows that women who give birth to their first child at 35 or younger tend to have a lower risk of breast cancer. In many countries, increasing numbers of women are now choosing to have children later in life or not at all, which could be reflected in cancer rates, Jemal says.

To help lower the risk of cancer, everyone can benefit from evidence-backed health advice like eating a balanced diet, getting plenty of exercise, and not smoking or drinking heavily. But, ultimately, each individual’s chance of getting cancer is different. People with specific risk factors—like genetic markers or a family history of cancer—should consult a doctor about early screening and other preventive measures, Barakat says. Getting a head start can be crucial, he adds, because people with genetic predispositions to cancer are often diagnosed fairly early in life.

It’s also important, Barakat says, to know your body and see a doctor if you think something is wrong. “When I look at some of the patients who were diagnosed with early-onset colorectal cancer, they had symptoms, but nobody thought that a 30-year-old had colon cancer,” he says. The longer it takes to detect cancer, the harder it may be to treat—so it’s important not to assume everything is fine just because you’re young and seemingly healthy.

Of course, every episode of gastrointestinal distress or bloating isn’t a sign of something serious; often, these issues are nothing more than uncomfortable. But if you’re having unusual symptoms that “continue for a long time, you definitely have to look into it,” Barakat says. “And doctors have to be more aware and be a little bit more suspicious.”