Floating or greasy stools: causes, red flags and when to get it checked

Stools floating on its own, without other changes, is common and is not usually a sign of disease. Gas trapped in the stool, a high-fibre meal or a short bout of diarrhoea can all make poo buoyant, and it often settles without anything being done.

What deserves attention is a combination: stools that float and look yellow or pale, are greasy or oily, smell unusually foul, and are hard to flush away, especially if this happens repeatedly. Guts UK describes this picture as a sign that dietary fat is not being absorbed well, and the NHS describes similar stools in coeliac disease and chronic pancreatitis. If it persists for more than a couple of weeks or comes with weight loss, tiredness or tummy pain, a GP should look into it.

Fat in food is normally broken down by bile from the liver and enzymes from the pancreas, then absorbed in the small bowel. Guts UK explains that the pancreas makes enzymes that convert fats into fatty acids and glycerol, and that undigested nutrients reaching the large bowel can produce fatty diarrhoea, wind, bloating and belly pain.

When fat escapes absorption it ends up in the stool. That makes the stool bulkier, paler or yellow, greasy and strong-smelling, and less likely to flush away. In severe cases, Guts UK says, oil can be visible on the surface of the toilet water.

It is the repeated pattern, not a single occasion, that points to malabsorption. People with ongoing steatorrhoea may also lose weight, feel tired, or develop deficiencies in vitamins and iron because the body is not taking in what it needs.

Several digestive conditions can interfere with fat absorption. The ones named in NHS and Guts UK pages are set out below.

The NHS describes coeliac disease as an autoimmune condition in which the immune system attacks the gut when you eat gluten, damaging the small bowel so the body cannot properly take in nutrients. It affects at least 1 in 100 people in the UK, and the NHS says milder cases may go undiagnosed or be mistaken for irritable bowel syndrome. It lists diarrhoea that may smell particularly unpleasant, stomach aches, bloating, tiredness, weight loss and an itchy rash among the symptoms.

Guts UK stresses one practical point for testing: do not stop eating gluten before seeing your GP, because the blood test needs you to be eating gluten to identify the antibodies. Going gluten-free first can make the test falsely reassuring.

On the pancreas side, the NHS says chronic pancreatitis is more common in people who drink or smoke heavily, and that there is no single test for it, so a GP may need to rule out other causes first. Guts UK explains that pancreatic exocrine insufficiency can follow pancreatic disease and that the most widely used test in the UK measures an enzyme called elastase-1 in a stool sample, which is simple to do but can miss mild cases.

The following features alongside floating or greasy stools make an early GP assessment more important.

• Stools that have become pale, grey or clay-coloured, particularly with dark urine or yellow skin or eyes. Guts UK says very pale or grey poo might mean a problem with the pancreas or liver, and the NHS says jaundice needs urgent medical help.

• Unintentional weight loss, loss of appetite or tiredness that does not improve.

• Pain in the upper tummy that goes through to the back or is worse after eating. The NHS lists pain at the top of the tummy and back, jaundice, loss of appetite and weight loss among the symptoms of pancreatic cancer, and says to see a GP if symptoms get worse or do not improve after 2 weeks.

• Black, tarry poo or blood in the poo, which needs prompt medical help.

• Diarrhoea lasting more than 7 days, or being sick for more than 2 days, according to the NHS, which says to get advice from NHS 111.

A GP will ask how long it has been happening, what the stools look like, what you eat and drink including alcohol, which medicines you take and whether you have lost weight. They may examine your tummy and check for jaundice.

Tests depend on the likely cause. The NHS and Guts UK mention a blood test for coeliac disease, blood tests for anaemia and other deficiencies, a stool test for infection or for inflammatory bowel disease, a faecal elastase test for pancreatic function, and imaging such as ultrasound or CT of the pancreas and bile ducts. Some people are referred for a gastroscopy.

Treatment is directed at the cause: a strict gluten-free diet for coeliac disease, enzyme replacement taken with food for pancreatic insufficiency, stopping alcohol and smoking for chronic pancreatitis, and medicine for bile acid diarrhoea. Guts UK says not to stop a prescribed medicine you suspect is responsible without talking to your doctor.

If your stools float occasionally, are otherwise a normal brown colour, are not greasy or especially foul smelling and you feel well, it is reasonable to keep an eye on things for a week or two. Making a note of any link to meals, drinks, medicines or a bout of diarrhoea can show a pattern.

Guts UK points out that people with irritable bowel syndrome can sometimes have symptoms after eating fatty food, which can be mistaken for fat malabsorption. Even so, if the stools stay oily or you are losing weight, it is sensible to have it checked rather than assume it is IBS.