Colorectal cancer red flags

At a glance

This page exists because we have a safety obligation to cover it clearly. If you have found this page, you may be worried about your symptoms. That is understandable.

The most important thing to know: most bowel symptoms are not cancer. Conditions like hemorrhoids, fissures, IBS, and other common issues cause the vast majority of the symptoms listed below. But certain patterns of symptoms do warrant a doctor’s assessment — and early assessment leads to better outcomes.

This page covers which symptoms to take seriously, who may be at higher risk, and what to do next. It is not diagnostic — only a doctor can assess your individual situation.

Symptoms that should prompt a doctor visit

The following symptoms should be discussed with a doctor, particularly if they are persistent (lasting more than a few weeks), new, or unexplained:

  • A persistent change in bowel habits — this might be going more often, less often, looser stools, or a change in the pattern that does not settle
  • Rectal bleeding — especially if it is new, persistent, dark, or mixed into the stool
  • Unexplained weight loss — losing weight without trying or changing your diet
  • Persistent abdominal pain or bloating — particularly if it is new and does not have an obvious cause
  • A persistent feeling that the bowel does not empty completely
  • New or worsening fatigue — especially alongside other symptoms on this list
  • Iron deficiency anaemia — sometimes detected through blood tests before other symptoms are noticeable

No single symptom on this list means cancer. But patterns — especially combinations of symptoms that persist — deserve prompt attention.

Who may be at higher risk

Certain factors are associated with higher risk. If any of these apply to you, it is worth being proactive about discussing symptoms with your doctor:

  • Age over 50 — risk increases with age, though colorectal cancer can occur at any age
  • Family history — a first-degree relative (parent, sibling, child) with colorectal cancer increases your risk. If multiple relatives are affected, or if they were diagnosed young, the risk is higher
  • Personal history of polyps or inflammatory bowel disease — conditions like Crohn’s disease or ulcerative colitis can increase risk over time
  • Increasing rates in younger adults — colorectal cancer in people under 50 has been rising. Do not dismiss symptoms because of your age

Having risk factors does not mean you will develop cancer. It means being aware and proactive is worthwhile.

Most symptoms are not cancer

It bears repeating: the symptoms listed above are far more commonly caused by benign conditions.

  • Changes in bowel habits are commonly caused by diet, stress, IBS, or medication changes
  • Rectal bleeding is most often caused by hemorrhoids or fissures
  • Fatigue has many causes, most of them unrelated to the bowel
  • Abdominal pain and bloating are extremely common and usually have straightforward explanations

The reason to see a doctor is not because these symptoms usually indicate something serious — it is because the small number of cases where they do indicate something serious benefit enormously from early detection.

What to do next

If you recognise any of the patterns described above:

  1. See your doctor. Describe your symptoms, how long they have been present, and any relevant family history.
  2. Do not wait for symptoms to get worse. Early assessment is always better than delayed assessment.
  3. Do not self-diagnose. Neither assuming it is nothing serious nor assuming the worst is helpful. A doctor’s assessment gives you clarity.
  4. Ask about screening. If you have risk factors, ask your doctor about screening options appropriate for your age and history.

What your doctor may do

When you see your doctor about these symptoms, they may:

  • Ask detailed questions about your symptoms, timeline, and family history
  • Perform a physical examination, which may include a digital rectal examination
  • Order blood tests, including checking for iron deficiency
  • Refer you for further investigation, such as a colonoscopy or flexible sigmoidoscopy
  • Reassure you if the assessment suggests a benign cause

A referral for further investigation does not mean your doctor thinks you have cancer. It means they want to be thorough — which is exactly what you want.

Talking to your doctor

If any of the following apply, make an appointment with your doctor:

  • You have persistent symptoms from the list above
  • You are over 50 and have not had a bowel assessment
  • You have a family history of colorectal cancer and have not discussed screening
  • You have symptoms that concern you, even if they seem minor

You are not wasting your doctor’s time. These are exactly the kinds of symptoms they want to hear about. Early conversations lead to early action, and early action leads to better outcomes.

When to seek care

If you experience any of the following, seek urgent medical care:

  • Persistent change in bowel habits lasting more than a few weeks
  • Rectal bleeding without an obvious cause
  • Unexplained weight loss
  • Persistent abdominal pain or bloating
  • Blood mixed into the stool
  • Dark or black stools
  • A feeling that the bowel does not empty completely
  • New or worsening fatigue without explanation

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