A stomach ache sends a 34-year-old and a 62-year-old to urgent care on the same afternoon. For decades, doctors treated those two visits very differently, because colorectal cancer counted as an older adult's disease. That assumption no longer holds up. Colorectal cancer diagnoses have been climbing in adults under 50 for years, even as rates in adults over 50 keep falling. Researchers do not have one settled explanation yet, but they have real leads, and you have real, doable steps to take starting today.
The numbers behind the headlines
According to the American Cancer Society, colorectal cancer rates in adults under 50 rose about 2.9 percent a year between 2013 and 2022[1]. Rates in adults 50 to 64 also rose, but far more slowly, about 0.4 percent a year over that same period. Overall colorectal cancer rates have been falling since the mid-1980s, largely because more people are getting screened.
A colonoscopy lets a doctor look inside your colon with a scope and remove small growths called polyps before they ever turn into cancer. Removing those polyps early is the main reason screening lowers cancer rates for the age groups that get screened regularly. Younger adults do not get that same protection nearly as often. Screening has historically started at 45 or 50, so most people under that age never get a colonoscopy unless a symptom sends them looking for one. And when a 30-year-old shows up with blood in their stool, hemorrhoids, stress, or diet often gets blamed first, since a cancer diagnosis at that age still feels unlikely to a lot of doctors.
How screening and symptoms differ by age
Age changes more than your cancer risk. It also changes how your symptoms get treated, from who gets screened automatically to how fast a worrying symptom gets investigated.
| Adults 50 and older | Adults under 50 | |
|---|---|---|
| Routine screening | Colonoscopy recommended on a regular schedule starting at 45[2] | No routine screening unless family history or symptoms prompt it |
| How symptoms get read | Blood in stool or bowel changes more often trigger a colonoscopy quickly | Same symptoms more often get attributed to hemorrhoids, stress, or diet first |
| Typical path to diagnosis | More often caught through routine screening, at an earlier stage | More often diagnosed after symptoms appear and get investigated |
This gap does not mean younger patients are simply unlucky. Doctors are increasingly aware of the pattern, and that awareness is helping shorten the time between a first symptom and a diagnosis.
What might be driving the rise
Nobody has found one single cause, and researchers studying this are upfront that it remains an open question. Some factors have more evidence behind them than others.
- Obesity, which raises colorectal cancer risk[2]
- Physical inactivity[2]
- A diet low in fiber and high in fat, processed food, and red meat[2]
- Family history of colorectal cancer or polyps, including inherited conditions like Lynch syndrome[3]
- A 2025 genomic study found that colibactin, a DNA-damaging toxin produced by certain E. coli strains, left a distinctive mutation signature in over half of colorectal cancers diagnosed before age 40, suggesting exposure to it early in childhood may set some cancers on an earlier timeline[4]
- Whether antibiotics, birth method, breastfeeding, or ultra-processed diets in early childhood shape which gut bacteria take hold, and whether that in turn affects colibactin exposure, is still being investigated[4]
The gut bacteria theory is promising, but it remains unproven. No test or treatment based on it exists yet, and the researchers studying it say the question is far from settled. For more on this connection, see Colorectal Cancer and Your Gut Microbiome.
Symptoms to take seriously at any age
Colorectal cancer is still rare in your 30s and 40s. That rarity works against you, since rare causes tend to get ruled out last, not first.
Watch for blood in your stool, a real change in bowel habits, ongoing abdominal pain, or weight loss you cannot explain[5]. Any one of these lasting more than a couple weeks is worth a call to your doctor, regardless of your age. Mention a family history of colorectal cancer or polyps too, since that can move up when your own screening should start.
What to do this week
If you are 45 or older and have never been screened, call your doctor's office this week and get a colonoscopy on the calendar. If you are younger and have a symptom that will not quit, do not wait to be offered a test: ask your doctor directly whether you should get one. Bring a simple note of when the symptom started and how often it happens, along with anything from what to bring to your first GI appointment; that small detail helps a doctor decide how urgently to act.
