SUBSCRIBE & SAVE Less than $3 per week View Profile The Explainer Talking Points The Week Recommends Newsletters From the Magazine The Week Junior Food & Drink Personal Finance All Categories Newsletter sign up under the radar A bacterial toxin could be contributing to the colorectal cancer rise in young people Most exposure occurs in childhood Newsletter sign up Theories explaining children's exposure to colibactin include early antibiotic use and consumption of processed foods (Image credit: Illustration by Julia Wytrazek / Getty Images) Devika Rao, The Week US 30 April 2025 Colorectal cancer has increased significantly over the past 20 years among adults under 50. Now scientists may have identified a potential factor in the rise: a toxin called colibactin. Exposure to the toxin happens in childhood and could be manipulating DNA to increase cancer risk. Toxin timeline Colibactin was linked to colorectal cancer cases in younger people, according to a study published in the journal Nature. The toxin has been known to cause DNA damage and is produced by several species of harmful gut bacteria, including E. coli. The recent study looked at tissue samples from close to 1,000 colorectal cancer patients across the world, and found that "around 50% of early-onset colorectal cancers in individuals under 40 carried the distinctive signature of colibactin exposure," said senior study author Ludmil Alexandrov, a bioengineering and cellular and molecular medicine professor at UC San Diego, to NBC News. Colibactin is called a "genotoxin" and is essentially the "weapon system of a bacteria to fight other bacteria and to defend themselves," said Alexandrov. It can "get directed" to the gut cells and seed mutations, increasing the risk of developing colorectal cancer, said NPR. Also, exposure to colibactin happens well before a cancer diagnosis, usually in early life. "Our estimate is that it happens within the first 10 years of life," Alexandrov said. "So if you get that mutation at age 5, that puts you 20 to 30 years ahead of schedule for getting colorectal cancer." Subscribe to The Week Escape your echo chamber. Get the facts behind the news, plus analysis from multiple perspectives. SUBSCRIBE & SAVE Sign up for The Week's Free Newsletters From our morning news briefing to a weekly Good News Newsletter, get the best of The Week delivered directly to your inbox. From our morning news briefing to a weekly Good News Newsletter, get the best of The Week delivered directly to your inbox. There are "several plausible hypotheses" as to how children can be exposed to colibactin, including "early-life antibiotic use, which may allow these strains to establish more easily; dietary shifts such as increased consumption of processed foods or reduced fiber consumption; increased rates of C-section births or reduced breastfeeding; and wider use of early group childcare which could facilitate microbial transmission during a critical developmental window," Alexandrov said. While the study linked colibactin to cases of cancer, it does not prove that the toxin actually causes it. Cancer causes Scientists have observed an alarming rise in colorectal and gastrointestinal cancers in people under 50 since the mid-1990s, but have not been able to pinpoint a specific cause. The disease's "incidence in adults under 50 has roughly doubled every decade for the past 20 years," said a release about the study. "If current trends continue, colorectal cancer is projected to become the leading cause of cancer-related death among young adults by 2030." So while colibactin is not a definitive cause, it could be an important piece of the puzzle. Previous studies had linked colibactin to colorectal cancer, but "either focused on late-onset cases or did not distinguish between early- and late-onset disease," said the release. Colibactin-producing bacteria are not the only toxin to have been linked to cancer, either. Exposure to the microbe F. nucleatum has also been found to potentially increase the risk of colorectal cancer development. "While colibactin-producing species may cause the initial mutations that drive tumor formation, F. nucleatum may contribute to disease development by enabling the tumor to proliferate and evade the immune system," said NBC News. Explore More health news Sign up for Today's Best Articles in your inbox A free daily email with the biggest news stories of the day – and the best features from TheWeek.com Contact me with news and offers from other Future brandsReceive email from us on behalf of our trusted partners or sponsorsBy submitting your information you agree to the Terms & Conditions and Privacy Policy and are aged 16 or over. Devika Rao, The Week US Social Links Navigation Devika Rao has worked as a staff writer at The Week since 2022, covering science, the environment, climate and business. She previously worked as a policy associate for a nonprofit organization advocating for environmental action from a business perspective. 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