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As a general rule, you are lucky to be living in 2026. It’s a good time to be alive.

You are, on average, healthier than any other humans who have ever lived, with alonger life expectancy, less infectious disease, and even lower rates of dying from most chronic diseases once we correct for age.

Canceris a great example of this. Cancer rates havebeen stable or fallingfor decades. Even better,cancer mortality– that is, how likely you are to die from cancer if you get it – has plummeted.

There are many cancers that were death sentences in the 90s which are nowconsidered a form of chronic diseaselikediabetesor emphysema due to new treatments.

There’s one place where the disease seems to buck this trend – colorectal cancer in young people.

While rates of colorectal cancer – which includes both colon and rectal cancers – havefallen overall, there’s been arecent uptickin cases in people under the age of 50, which is considered young when it comes to cancer.

This has almost no impact on the total number of colorectal cancer diagnoses, because the absolute number of people getting colorectal cancer at young ages is still very low.

However, it’s a very confusing finding.

Rates of colorectal cancer are generally abit lower in older people, but rising in younger people, and we have no good idea why that’s happening.

There are, of course, some proposed explanations.

Some people point topesticides or herbicideslike picloram, whichhave been linkedto colorectal cancer risk. There are two problems with this idea.

“While rates of colorectal cancer – which includes both colon and rectal cancers – have fallen overall, there’s been arecent uptickin cases in people under the age of 50 which is considered young when it comes to cancer. ” – Gideon Meyerowitz-Katz, Epidemiologist

For one thing, picloram and many other chemicalsare used a bit lesstoday than they were in the 80s and 90s. It’s unclear how those chemicals could cause more cancer in a specific age group in the 2020s even though they aren’t being used as much as they used to be.

Also, older people tend to havemore exposureto these chemicals. This makes sense – regulation was much looser in past decades and it’s quite likely that your parents had more pesticides in their food than you do.

It makes no sense for colorectal cancer to be increasing in young people but decreasing in older people if this sort of environmental issue is to blame.

The same general problem holds true for many environmental exposures. Peoplehave linkedper- and polyfluoroalkyl substances (PFAS, often called ‘forever chemicals’) tocolorectal cancer.

Again, however, exposure to PFAS isnot neatly divided by ageand in some cases older people may have been far more exposed to these chemicals than the younger group who is getting more cancer.

It’s hard to find an exposure that could explain this increase.

Most of the things that we know are possible causes of colorectal cancer are more common for older people than younger ones. There are very few environmental issues that are more common now than they were when older generations were growing up.

Another potential explanation is obesity. We know thatobesity causes more colorectal cancer, and younger people are definitely more obese now than they were in the past.

Again, this is not a compelling explanation becauseolder people are also more obese, so it can’t be the only impact on cancer risk. Modeling suggests thatat most 15 percentof colorectal cancer is explained by people gaining weight, perhaps less.

The colorectal cancer mystery is made more confusing by the fact that the trend is not consistent across countries. It’s not even consistent in groupings of countries.

A 2019 studyfound that colorectal cancer rates in young people were stable or decreasing in nearly half of the countries analyzed.

A more recent study from 2025had similar findings. This just muddies the water further – it’s unclear what could be causing colorectal cancer rates to increase in young people in the UK and US but decline in Italy and Lithuania.

Perhaps the most likely explanation of all of this complexity is that it’s all down to testing.

While we know that screening recommendationsare unlikelyto be the main reason for the increase – if nothing else, screening recommendations have only recently changed to include younger age groups but the trend has been going since the 90s – but these aren’t the only changes to the healthcare system in recent decades.

It could be that young people are simply more likely to get a test for colorectal cancer for all sorts of reasons, and that this has impacted the number of people who get diagnosed.

It’s also possible that the trend is related to how countries report data. When we talk about disease statistics, we are always talking about themeasuredrate of a condition. Cancer registries have been improving for a long time, which may be part of the reason that younger people are being recorded as having more cancer.

However, even these explanations are not that convincing. It’s hard to understand how they could impact younger people and older people in different ways.

There is definitely an increase in recorded rates of colorectal cancer in young people in some countries, but the reason remains a bit of a mystery. We know that many explanations are a bit unlikely, but the true cause is very hard to identify.

Gideon Meyerowitz-Katzis an epidemiologist working in chronic disease in Sydney, Australia. He writes a regular healthblogcovering science communication, public health, and what that new study you’ve read about actually means.He’spreviously helped ScienceAlertbreak down the real science behind the mostviral papers.