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Researchers have theories regarding the increasing incidence of colorectal cancer in younger adults, even as rates decline in older populations.(Image credit: SDI Productions via Getty Images)Share this article 0Join the conversationFollow usAdd us as a preferred source on GoogleSubscribe to our newsletter
An unusual trend is emerging in colorectal cancer diagnoses: While the incidence of the disease is decreasing among older individuals, who are typically at higher risk, it is on the rise among those under 50.
These diagnoses are often devastating, as younger individuals also tend to experience a longer interval between the onset of symptoms and receiving a diagnosis, meaning most of their cancers are detected at a late stage that is more challenging to treat.
But what is contributing to this surge in young people? Medical professionals and scientists suspect that a change occurring post-1960s is responsible, possibly related to alterations in people’s environments or lifestyles. Offering a potential clue, recent studies also indicate that whatever the factor, it primarily impacts cancers affecting the rectum and the lower section of the colon.
The rise of colorectal cancer in young adults
Approximately 158,850 new cases of colorectal cancer were diagnosed in the U.S. in 2026, according to the American Cancer Society (ACS). More than 86,000 of these cases — over half — occurred in individuals aged 65 and older. However, these figures represent a yearly decrease of 2.5% in this demographic since 2013.
Medical experts attribute the reduction in colorectal cancer among those 65 and older to the effectiveness of screening methods, according to Dr. Aasma Shaukat, a gastroenterologist at NYU Langone Health. Through routine colonoscopies, which commence at age 45 for individuals at average risk, doctors can identify and remove precancerous polyps, thereby preventing their transformation into cancer.
Concurrently, while the incidence in those over 65 has declined, individuals between 50 and 64 have experienced a 0.4% annual increase, and those aged 20 to 49 have seen a more concerning surge of 3% annually. This upward trend is observed across all racial and ethnic groups.
Consequently, as indicated by research published in the CA: A Cancer Journal for Clinicians by the ACS, there are 24,640 new cases annually for individuals 49 and younger, and 47,600 new cases annually for those aged 50 to 64.
The majority of these cases are classified by physicians as “left-sided” cancers, originating in the lower colon, which follows the left side of the body, and the rectum. From 1999 to 2023, rectal cancer mortality increased two to three times more rapidly than colon cancer mortality across all demographics, according to findings presented in May at Digestive Disease Week 2026, a prominent gastroenterology conference.
Standard colonoscopies are recognized for their role in helping to reduce colorectal cancer rates in older adults.
(Image credit: PonyWang via Getty Images)Potential environmental influences
Cancers develop due to genetic mutations, some of which occur randomly during cell division. The cells lining the gut divide continuously, with the entire colon lining regenerating weekly, as noted by Shaukat. The body possesses mechanisms to correct the numerous DNA errors that arise during this turnover, but when the rate of errors escalates too rapidly or when repair processes falter, colorectal cancer typically emerges.
The intestinal environment can impact both the error rate and the effectiveness of cellular repair. Researchers have discovered a complex interplay between the gut microbiome, which refers to the community of microorganisms in the colon, and health factors such as diet, physical activity, and insulin sensitivity.
Inflammation also plays a role in this dynamic. While inflammation is a crucial immune response that facilitates tissue repair through new cell growth, persistent inflammation can render dividing cells susceptible to mutations and uncontrolled proliferation, ultimately leading to cancer.
The factors contributing to increased chronic inflammation are numerous, Dr. Theodore Levin, a researcher and clinical lead for colon cancer screening at Kaiser Permanente Northern California, informed Live Science. However, he cautioned that “these are all thoughts or hypotheses.”
One contributing factor is the rise in sedentary lifestyles and obesity, which fosters insulin resistance and, consequently, disrupts the microbial communities residing within the intestines. These microbes assist in digestion and produce compounds that can either mitigate or exacerbate inflammation.
The use of antibiotics in childhood has increased since the 1960s, which can also disturb the gut microbiome. Furthermore, dietary shifts that affect the microbiome since the 1960s include a rise in sugar-sweetened beverages, as mentioned by Levin, along with the introduction of a greater variety of ultra-processed foods, which generally have lower fiber content compared to fresh fruits and vegetables. Fiber, he noted, supports a diverse gut microbiome that tends to reduce inflammation. (Research also suggests that fermented foods have a similar effect.)
Researchers are also concerned about the widespread presence of plastics, Levin added.
Some laboratory investigations suggest that colorectal cancer cells can absorb microplastic particles, and this absorption enhances the cells’ capacity to spread, at least within a laboratory setting. This could imply that microplastics increase the likelihood of cancer metastasizing throughout the body. Additionally, certain animal studies indicate that microplastics impair immune function, which could theoretically enable cancer cells to evade the body’s defenses.
Plastic particles may also transport carcinogenic substances deep into the digestive tract, Levin suggested. While research is still ongoing, some evidence links prolonged exposure to perfluorooctanesulfonic acid (PFOS), a type of “forever chemical” found in nonstick cookware and firefighting foams, to an elevated risk of colorectal cancer. Experiments using mouse intestinal tissue have demonstrated that PFOS diminishes a gut enzyme that provides protection against cancer while simultaneously promoting the production of proteins that encourage tumor development.
“I don’t know if it would have been as aggressive if they had caught it a year-and-a-half earlier.”
Jenna Scott, a 40-year-old cancer patient in Atlanta
However, researchers have yet to identify a definitive cause, cautioned Michael Sapienza, CEO of the non-profit Colorectal Cancer Alliance. For instance, the findings from observational studies examining the link between exposure to forever chemicals and colorectal cancer rates are inconsistent, with some studies even suggesting that higher levels of PFOS in the blood are associated with fewer colorectal cancer cases.
Therefore, while numerous hypotheses exist, the evidence remains unclear. Older adults are also subject to these environmental and lifestyle changes, prompting researchers to investigate why their cancer rates are not mirroring the increase seen in younger individuals. It is possible that the removal of precancerous lesions during colonoscopies is masking a similar rise in the older demographic. Alternatively, early childhood exposure might be the most critical factor, a risk that the oldest adults were less exposed to.
Raising awareness of the symptoms
Scientists are not entirely certain why cancers affecting the lower colon and rectum are increasing at a faster pace than “right-sided” cancers located in the upper intestines.
The lower and upper sections of the colon are significantly different, Levin explained, even originating from distinct embryonic structures during the earliest stages of development. Cancers on the right and left sides often exhibit different genetic mutations. Left-sided colorectal cancer frequently develops due to what researchers term chromosomal instability, which involves errors in chromosome segregation during cell division when cells replicate their DNA. Right-sided cancers are more prone to developing from issues with DNA repair mechanisms during replication.
These distinct pathways could assist researchers in connecting environmental and lifestyle factors to the cellular changes that lead to colorectal cancer. However, this research requires time. For the present, gastroenterologists are focused on increasing awareness of the disease’s symptoms and ensuring that other healthcare providers consider testing younger patients for cancer.
Initial symptoms may include rectal bleeding, unintended weight loss, anemia, abdominal discomfort, blood in the stool, alterations in bowel movements, and unexplained nausea and vomiting. Unfortunately, many early indicators of colorectal cancer overlap with symptoms of far less serious conditions. For example, rectal bleeding can be attributed to hemorrhoids, and changes in bowel habits can result from various factors, ranging from stress to infections.
Jenna Scott, a 40-year-old resident of Atlanta, was 29 and pregnant when her symptoms began. She did not receive a diagnosis until she was 31. By that point, the cancer had metastasized, spreading to other organs. Scott continues to undergo treatment.
“I don’t know if it would have been as aggressive if they had caught it a year-and-a-half earlier,” she conveyed to Live Science.
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Scott’s initial symptom was rectal bleeding, but her physician dismissed it as hemorrhoids associated with pregnancy. Another characteristic symptom of colorectal cancer, weight loss, seemed like typical postpartum fluctuations. Healthcare systems and organizations like the Colorectal Cancer Alliance are working to enhance awareness among physicians across all specialties, encouraging them to thoroughly investigate these symptoms in young individuals rather than attributing them to less serious causes.
Although routine colorectal cancer screenings are not recommended until age 45, patients should assertively advocate for earlier testing if they experience any indicative symptoms, according to Sapiena.
“It does not automatically mean you have colorectal cancer,” Sapiena stated regarding these symptoms. “But it does signify that you need to be your own advocate” and seek screening promptly.