March is Colorectal Cancer Awareness Month, and colorectal cancer remains one of the most common cancers worldwide. The good news? It is also one of the most preventable, especially when detected early.
Let’s be honest — most of us flush and forget.
We rarely look. We definitely don’t talk about it. And we assume that as long as we’re “going regularly,” everything is fine.
But your poop/ stool is one of the simplest, most accessible health indicators your body gives you every single day. Changes in colour, shape, size or frequency can reflect your diet and hydration. But sometimes, they may signal something more serious, including colorectal cancer.
So, before you flush next time, here’s what you should know.
Why Does Colon Cancer Affect Stool Appearance?
The colon plays an essential role in processing digested food, absorbing water and forming stool for elimination. When a cancer develops in the colon, it can interfere with this normal process in several ways:
- A growing tumour may partially block the passage of stool, altering its shape or size.
- Cancer can cause bleeding within the colon, leading to visible or hidden blood in the stool.
- It may disrupt normal bowel movement patterns, causing persistent diarrhoea or constipation.
- In more advanced cases, obstruction can significantly affect stool passage.
Because stool passes directly through the colon, changes in bowel habits or stool appearance may sometimes serve as warning signs — particularly as the disease progresses.
Nevertheless, in its early stages, colorectal cancer often does not cause any noticeable symptoms. This is why regular screening is so important, even if you feel completely well.
What Does Healthy Poop Look Like?
Healthy stool is generally:
- Medium to dark brown in colour (due to bile pigments)
- Soft, smooth and well-formed (sausage-shaped)
- Easy to pass without straining
- Consistent in pattern over time
The Bristol Stool Chart, a medically recognised tool, classifies stool into seven types. Types 3 and 4 (smooth, soft, sausage-like stools) are considered ideal.
Poop Colour: What It Could Mean
Colour changes are often harmless and related to food or medication — but some warrant attention.
Brown/ light brown/ dark brown – Normal and healthy.
Green – Often linked to veggie-rich diet or faster digestion
Yellow – May indicate fat malabsorption or pancreatitis if persistent.
Red – Could be from haemorrhoids, but may also indicate gastrointestinal bleeding (unless due to certain red foods)
Black – May signal upper gastrointestinal bleeding (unless due to iron supplements or certain medications)
Pale or clay-coloured – Could suggest bile blockage or liver issues
If unusual colours persist or occur without a clear dietary reason, seek medical advice immediately.
What Signs Should You Look Out For?
Early colorectal cancer may not cause noticeable symptoms. However, the following stool-related changes can be warning signs:
- Blood in the stool
You may notice bright red blood, which often originates from the lower colon or rectum. Dark, black or tar-like stools may indicate bleeding higher up in the colon. Any unexplained bleeding should be evaluated. - Thin or pencil-like stools
If a tumour narrows the colon’s passageway, stools may become persistently ribbon-thin or pencil-shaped. - Pellet-like stools (Type 1 on the Bristol Stool Chart)
Persistent pellet-like stools (especially when accompanied by abdominal pain or bloating) may suggest bowel obstruction and should be medically evaluated. - Changes in bowel frequency
Diarrhoea or constipation lasting more than a few days without a clear cause should not be ignored. - Increased mucus in stool
Stool often contains a small amount of mucus, a jellylike substance, that your intestines make to keep the lining of your colon lubricated. However, noticeable increase in amount of mucus in stool may warrant medical advice.
Other Conditions That Can Cause Similar Symptoms
Not all stool changes are caused by cancer. Other conditions that may produce similar signs include:
- Haemorrhoids
- Anal fissures
- Inflammatory bowel disease (such as Crohn’s disease or ulcerative colitis)
- Gastrointestinal infections
- Certain foods or medications
Because symptoms can overlap, seeking professional assessment is important.
When Should You See a Doctor?
Consult a healthcare professional if you experience:
- Red or black stools
- Persistent thin or ribbon-like stools
- Persistent pellet-like stools
- Diarrhoea or constipation lasting more than a few days
- Ongoing abdominal pain
- A feeling of incomplete bowel emptying
- Unexplained fatigue or weight loss
Early evaluation allows serious conditions to be ruled out or detected at a treatable stage.
The Importance of Regular Screening
Colorectal cancer often develops silently, especially in its early stages. This is why regular screening is essential — even if you feel completely well.
Screening tests are designed to detect precancerous polyps or early-stage cancer before symptoms appear.
Two common screening methods include:
- Faecal Immunochemical Test (FIT)
A simple, non-invasive test that detects hidden blood in the stool. It can be done at home and is typically performed annually for individuals at average risk. - Colonoscopy
A more comprehensive examination that allows direct visualisation of the colon and rectum. Polyps can be removed during the procedure, preventing progression to cancer.
Health Promotion Board recommends routine colorectal cancer screening for individuals aged 50 and above. Those with additional risk factors, such as family history, may require earlier or more frequent screening.
Under the Healthier SG initiative, Singapore Citizens and Permanent Residents aged 50 and above who are enrolled can benefit from free or subsidised colorectal cancer screening (FIT test) when referred by their enrolled clinic.
If you have not enrolled in Healthier SG, enrol with us today or speak to your Fullerton Health GP to learn more about the benefits available to you.
For more information about Healthier SG, visit: https://www.fullertonhealth.com/sg/services/healthier-sg/
Reviewed by: Dr Marcus Lee, Family Physician and Designated Workplace Doctor at Fullerton Health Singapore.
Reference list:
- Clinic, C. (2025). Stool (Poop) Color: Guide, What It Indicates, Healthy Color. [online] Cleveland Clinic. Available at: https://my.clevelandclinic.org/health/articles/stool-poop-color. [Accessed 27 February 2026]
- Mayo Clinic. (2025). Colon cancer stool: What to look for and how to test at home. [online] Available at: https://www.mayoclinic.org/diseases-conditions/colon-cancer/in-depth/colon-cancer-stool/art-20586915. [Accessed 27 February 2026]
- Ministry of Health. (2026). Screening Test Review Committee Report 2026, Volume 1. [online] Available at: https://www.moh.gov.sg/others/resources-and-statistics/strc-2026-volume-1/. [Accessed 27 February 2026]
- World Health Organization (2023). Colorectal Cancer. [online] World Health Organization. Available at: https://www.who.int/news-room/fact-sheets/detail/colorectal-cancer. [Accessed 27 February 2026]