Bowel cancer is the second most common cancer in both men and women in Australia and is more common in people over the age of 50. Rectal bleeding is the most obvious symptom of bowel cancer, also known as colorectal cancer, but other signs may be far more subtle. If you notice any of the following signs, talk to your doctor.

You learn you’re anaemic

A diagnosis of anaemia may be the first sign that you’re bleeding internally, even if you haven’t seen any other bowel cancer symptoms. “If a woman is menstruating, anaemia is less likely to be followed up with additional tests to see if it could be something else, like bowel cancer,” says cancer specialist Dr Randall Holcombe. “If a man is anaemic, you assume he’s bleeding from somewhere.” It’s not uncommon for people to bleed internally for up to six months before anything shows up in the stool, says Dr Patricia Raymond, a university fellow in Gastroenterology. If you experience any signs of anaemia, such as fatigue, skin pallor or dizziness, see a doctor, as they can also be bowel cancer symptoms.

You can’t catch your breath

Another side effect of a slow internal bleed is shortness of breath. If you aren’t bleeding aggressively or vomiting blood, your body puts more plasma in the blood without making more iron or red blood cells, says Dr Raymond. This prevents you from losing blood in large volumes but reduces your blood’s ability to carry oxygen, which is why you might be short of breath – one of the overlooked bowel cancer symptoms.

You feel bloated or crampy

“If things are starting to get blocked and backed up in the colon, you may experience bloating,” says Dr Holcombe. If you’re feeling a little puffy or crampy, there are many other factors that may be to blame, but if stomach symptoms persist, it could be a symptom of bowel cancer. If you start to notice a constant pain in the right side of your abdomen, that may mean the disease is in the later stages and has spread to the liver, he says.

You have severe constipation

A bout of constipation here and there is probably nothing to worry about, but if it becomes severe and persistent, it could be one of the symptoms of bowel cancer. “This is suggestive of some sort of obstruction, and if it seems to be there all the time, you should get it checked out,” says Dr Holcombe.

You pass skinny stools

Pay attention to what’s in the toilet, even if you don’t see blood – it can reveal lesser-known bowel cancer symptoms. If your stool consistently takes on a very narrow or skinny shape when it was previously chunky, that could point to a restriction in the colon caused by polyps, says Dr Raymond. Persistent diarrhoea may also be one of the symptoms of bowel cancer.

Your stool is a strange colour

Bleeding from the rectum may not always come in the form of bright red blood, says Dr Holcombe. Dark, tarry stools are a sign there’s probably some blood in there, and while it could be caused by something less serious, like an ulcer, this can also be one of the symptoms of bowel cancer, he says.

Written by Alyssa Jung. This article first appeared in Reader’s Digest. For more of what you love from the world’s best-loved magazine, here’s our best subscription offer.