Stool colours: what's common and what to tell a doctor

Stools come in many shades of brown, and an odd colour now and then is often down to something you ate. A few colours, though, are worth telling a doctor about straight away.

By The family behind Stool Log · Reviewed 5 November 2026

Brown, in any shade

Light brown to dark brown is the usual colour. Stool colour depends on what you eat and on bile, a yellow-green fluid that digests fats. As bile passes through your gut it changes from green to brown.¹

Green

Green stools often follow green leafy vegetables or green food colouring, such as in drink mixes or ice lollies. Iron supplements can do it too. Green can also happen when food passes through quickly, for example with diarrhoea, so bile doesn't have time to break down.¹

Yellow

Yellow, greasy, foul-smelling stools can follow fatty foods, such as deep-fried food. They can also mean there's too much fat in the stool because it isn't being absorbed well, for example with coeliac disease.¹ If it keeps happening, mention it to a doctor.

Black

Iron supplements, bismuth (the active ingredient in Pepto-Bismol) and black liquorice can turn stools black.¹

Black stools can also be a sign of bleeding higher up in the gut, such as in the stomach.¹ If there's no food or medicine to explain it, ask for an urgent appointment (see the box below).

Red

Beetroot, cranberries, tomato juice or soup and red food colouring can make stools look red. Bright red can also mean bleeding lower down, in the large bowel or back passage, often from piles.¹

Pale, white or clay-coloured

Pale, white or clay-coloured stools can mean a lack of bile, which may point to a blocked bile duct. Some medicines can also do it, such as antacids with aluminium hydroxide, large doses of bismuth, and barium used for X-rays.¹ Tell a doctor about pale stools you can't explain.

Writing it down

If you see an unusual colour, note the date, the colour, what you ate and any medicines in the day before, and whether it happened again. A stool diary with the Bristol type and colour gives your doctor a clear picture instead of a memory.

This article is general information, not medical advice. Talk to a doctor or nurse about your own symptoms.