The research, published in The Lancet Gastroenterology and Hepatology earlier this month, has prompted calls for a change in the screening guidelines for Australia's second most deadliest cancer.

Professor Graham Newstead, Director of Bowel Cancer Australia, says regular screening tests should begin in the 40s, with the peak body recommending the guidelines lower the age from 50 to 45.

The study has confirmed a trend colorectal surgeons have witnessed over the past 10 years, he said.

"My colleagues and I, we are all seeing younger people with bowel cancer in larger numbers," Prof Newstead told AAP.

"People need to take notice."

The study, conducted by a team of international researchers, found the incidence of colon cancer in people aged 20-29 had increased by 9.3 per cent per year between 2004 and 2014, while the rate of rectal cancer had increased by 7.1 per cent per year from 1993 to 2014.

Meanwhile, rates for people aged 50 and over have remained steady or decreased.

Now, almost one in 10 new cases occur in Australians under 50, with the majority of those diagnosed between 40 and 49 years of age.

Researchers have pointed to diet and lifestyle factors as possible reasons for the increase, including obesity, alcohol consumption, smoking, excessive consumption of red meat and decreased physical activity levels,

The study also stated evidence for antibiotic use during childhood, which alters gut microbiome, as a risk factor.

"It's also occurring in people who don't have a family history," Prof Newstead says.

"What the hell is going on?"

While the exact cause remains unknown, the surgeon has advised Australians to dig into their family history and go to the GP if there are any symptoms such as rectal bleeding.

"As mild as the symptoms might be, make sure it's not due to anything sinister," he says.

"We don't like to talk about bowels, there's the yuck factor, but it's important. This cancer is preventable."

Australian Associated Press