The colour and consistency of your stool can tell you a lot about your health. Getting into the habit of checking might not seem like a particularly fun task, but picking up on sudden changes in colour can help you to understand how your digestive system is functioning.
Taking the time to check for things like the sudden appearance of blood may help you to catch some medical conditions before they can progress and become more serious.
Don’t be alarmed if you check your stool and notice that it’s suddenly become green or yellow - there’s often an explanation for a dramatic change in colour, and you don’t need to panic if you notice something out of the ordinary.
There are some colours that should worry you though. Black or red stools can be a sign that you are bleeding from the stomach, intestines or oesophagus, while yellow or green poop can be symptomatic of an obstruction of the bile duct, which is the small tube that carries bile from the liver to the small bowel.
Relatively small changes to the colour or consistency of your stool can be caused by medical conditions like Crohn's disease, or more common illnesses like gastritis, so it’s always worth knowing what colour your poop should be, and why it can suddenly change.
When to worry
In many cases, coloured stools are caused by:
- Food you’ve eaten
- New medications
- A mild condition like haemorrhoids
That said, it’s important to understand the difference between harmless changes in colour, and the signs of a serious medical condition.
Yellow or green poop on its own can just be caused by food moving through the digestive tract too quickly, but frequently passing pale yellow stool could be the result of a fat absorption problem, or a blockage in your bile ducts. Knowing when to seek medical attention can help to ensure that serious problems are treated properly.
If you find that your stool is an odd colour, and the colour doesn't disappear after one or two days, you should book an appointment with your doctor.
You should also seek medical attention if your poop changes colour, and you start to experience other symptoms, such as abdominal pain, vomiting, weight loss, dark urine, swollen ankles, or yellowing of the skin or eyes.
Here, you can read more about the different colours of stool, and what they could mean. You’ll also find information that will help you to understand the consistency of your stool.
Black or very dark brown stool can be a sign that you are bleeding from your stomach or oesophagus.
When you bleed from the upper parts of the gastrointestinal (or GI) tract, the blood is broken down as it moves through your digestive system and enzymes start to break down your red blood cells.
This process produces a distinctive type of black stool, called ‘melaena’. In most cases, melaena will be:
- Jet black
It may also have a different smell, due to the breakdown of compounds in your blood.
According to medical publications like Clinical Methods, peptic ulcers are the most common medical cause of black stool. Other conditions that can make your stool black include:
Common causes of black or dark-brown stool also include iron supplements, antacids like Pepto-Bismol, or dark foods like blackberries or black liquorice which contain coloured pigments that can dye your poop.
If you have just started taking an iron supplement or using an antacid that contains bismuth, your stool may become grey or greenish-black. This might seem alarming, but try not to worry. The change in colour is most likely caused by unabsorbed minerals with a strong natural colour. If you are concerned, please see your doctor.
If your stool has turned black, and you’ve noticed a change in the texture or smell, you should go to hospital immediately. You should also go to hospital immediately if your stool has been black on more than one occasion.
Your doctor will be able to check for any serious medical conditions, and explain why your stool has turned black.
Yellow stool can be relatively common, and there’s no need to worry if you pass the occasional yellow poop.
Food colourings, sweet potatoes, and carrots can all dye your stool a strange shade of yellow, and it’s important to note that your poop will be yellow if you haven't had time to digest your food properly.
This means that conditions like diarrheoa could also turn your stool yellow for a day or two.
That said, yellow, grey or pale stool can be a sign that your body isn’t digesting fats properly, and you should seek medical attention if your stool is yellow on more than one or two occasions.
Healthy stool is brown because it contains a substance called bilirubin, which is added to your bile in the gallbladder, and then mixed into your stool to produce the colour that you’re familiar with.
Any condition that prevents bilirubin or bile from getting into your digestive system can cause your stool to turn pale. This includes conditions that block the bile ducts, such as:
It also includes any conditions which interfere with the production of bile, such as liver disease.
Conditions that prevent your body from absorbing fats can also cause yellow stool. This includes conditions like:
If your stool is yellow for more than one or two days, you should book an appointment with your doctor immediately. You should also book an appointment with your doctor if your stool is yellow, with a greasy texture or a foul smell.
Your doctor will be able to rule out serious medical causes, and help you diagnose the cause.
Noticing a green stool can be alarming, but there are a number of perfectly harmless reasons for your poop to take on a greenish hue.
Iron supplements can sometimes make your stool look green, as can the chlorophyll in dark green vegetables like broccoli, kale, or arugula (rocket). Food colourings can also dye your stool green, so if you’ve eaten a lot of green food recently, or started taking an iron supplement, you probably don’t need to worry too much.
Changes to the bacteria living in your gut can also make your stool green. These changes are often caused by antibiotics, and tend to resolve themselves after you have finished the full course of your medication.
Consistent green stool can be a sign of a medical problem, however.
Bile, which helps your body to digest fat, is green when it first enters the digestive system. As waste matter moves through your intestines, chemical reactions break down your bile and give it the brown tint which turns your stool its familiar colour.
When the digestive process happens too quickly, your bile can’t be broken down, and it retains its green colour. This can be one of the causes of green stool.
As a result, green stool can be a sign of a problem that’s causing your body to push food through your digestive system before your body has had time to digest it properly. This includes conditions like:
You should book an appointment with your doctor if you notice green stool on more than one occasion, and you:
- Haven't taken antibiotics recently
- Haven't started a new iron supplement or multivitamin
- Don’t eat a lot of leafy, green vegetables
Your doctor will be able to diagnose the cause, and help to rule out any serious medical conditions. You should also book an appointment with your doctor if you have green stool, and begin to experience nausea, or an upset stomach.
Bright red stool
Red poop can be a sign that there’s blood in your stool.
Blood in your stool can also be a sign that you’re bleeding from the lower gastrointestinal tract. This can be a sign of more serious medical conditions, including:
- Bowel cancer
- An anal fissure
- An anal fistula
- Inflammatory bowel disease
- Bowel polyps
- A sexually transmitted infection (STI)
- A tummy bug (gastroenteritis)
- Too high a dose of a blood-thinning medication
The presence of blood in your stool can also be a symptom of a relatively common, but mild condition, such as haemorrhoids, which occur when blood vessels in the anus become enlarged or irritated, and burst during a bowel movement.
If your stool is bright red, purple or maroon, you should see a doctor as soon as possible. They will be able to rule out serious medical conditions.
Although you should always see a doctor urgently if you develop blood in your stool, there are some harmless causes of bright red stool. Cranberries, beets, tomatoes and red peppers all contain coloured pigments that get passed through your digestive system, and end up in your stool. If you eat a lot of these foods, you may find that your stool becomes red or purple.
Certain medications - including the antibiotic amoxicillin - can also dye your poop red in the digestive tract. This is a natural side effect of taking these medications, and won’t cause you any harm.
White or pale stool
White or pale stool can also be a sign that your body isn’t producing enough bile. As mentioned in the section on yellow stool, your poop is brown because bile gets mixed into your food as it moves through the digestive system.
Bile helps the body to break down fats, but it's also broken down as it moves towards the large intestine, which alters its colour, and gives your stool its characteristic brown colour.
If your body isn’t producing enough bile due to a problem with the pancreas, the gallbladder, or the tubes that deliver bile to the small intestine, your stool will be colourless, pale, or a light shade of yellow.
This could mean that you are suffering from:
In most cases, stool that is white or pale because it lacks bile will also have a clay-like texture. It may be accompanied by symptoms like abdominal pain, fever, or nausea.
If you notice that you are passing white or pale stools, you should book an appointment with your doctor as soon as you can. They will be able to rule out any serious medical conditions, and help you to diagnose the change in colour.
What about consistency?
A change in the consistency or texture of your stool can also be alarming, particularly if you’re used to regular bowel movements. If you’re wondering why your poop is suddenly mushy or liquid, you’ll find more information in this section.
The Bristol stool chart
The Bristol stool chart is a reference guide that’s used to help people understand the consistency of their stool. It categorises seven different types of stool, as follows:
Hard stool is often a sign of constipation. Constipation occurs when the stool sits in your colon for too long and your colon absorbs so much water from the stool that it becomes hard and dry. Common causes of constipation include:
- Not eating enough fibre, such as fruit, vegetables and cereals
- A change in your routine or lifestyle, such as a change in your eating habits
- Ignoring the urge to pass stools
- Side effects of certain medications
- Not drinking enough fluids
Constipation can usually be treated by making small changes to your diet or lifestyle, but if constipation is bringing you discomfort or you have been passing hard stools for more than two weeks, you should book an appointment with your doctor.
Cracked stool can be a sign of dehydration, or a sign that stool is passing through your digestive system too slowly. When this happens, your colon will start to reabsorb water from your stool, making it appear cracked and hard.
If you are passing cracked stools, and are also:
- Feeling thirsty and lightheaded;
- Having dark coloured, strong-smelling urine; and
- Passing urine less often than usual
You are most likely dehydrated. Treating dehydration is relatively straightforward. In most cases, drinking plenty of fluids, such as water, semi-skimmed milk, diluted squash or fruit juice will be enough to remedy the problem.
If you are having trouble drinking enough, you should seek medical attention.
Mushy stool is often indicative of diarrhoea. Diarrhoea can be caused by stress, anxiety, medications, or a food allergy, but the condition is more commonly caused by gastroenteritis. Other causes include long-term health conditions like:
- Irritable bowel syndrome (IBS)
- Inflammatory bowel disease
- Coeliac disease
- Poor absorption of bile acid
- Chronic pancreatitis
- Diverticular disease
- Bowel cancer
If you suffer from frequent diarrhoea, you should book an appointment with your doctor, and talk to them about your concerns. They will be able to test for the conditions listed above, and help you work out why your stools are looser than they should be.
Liquid stool is caused by irritation in the small intestine, which forces the body to flush out the contents of your digestive tract before it’s had time to digest it properly, or absorb the liquid contents.
If you are passing liquid stools, you may be suffering from viral gastroenteritis, food poisoning, or a chronic condition like:
You should book an appointment with your doctor, so that you can determine the cause. You should also take steps to ensure that you stay properly hydrated, as passing liquid stool can cause you to become dehydrated.
If your stools float, it is because they contain too much gas or fat. This could be the result of flatulence, which develops when you eat foods that contain a lot of complex sugars. These sugars have to be broken down by bacteria in the small intestine, and produce a lot of waste gasses when they are processed.
Foods that are known to cause flatulence include:
- Whole grains
- Vegetables like brussels sprouts, broccoli or cabbage
- Fizzy drinks
- Hard sweets
Excess gas or fat can also be a sign of some malabsorption problems. Coeliac disease, Crohn's disease, liver disease, and some forms of cancer can all prevent your body from breaking down certain nutrients, triggering the build-up of waste gasses, and causing your stools to float.
If you find that your stools are floating for more than one or two days, you should book an appointment with your doctor. They will be able to help you diagnose the cause, and treat the problem properly.
Oddly-coloured stool isn’t always a cause for concern, but you should check for ongoing changes in the colour, consistency, or texture of your poop. This will help to make sure that you’re aware of any changes, and enable you to seek medical attention whenever appropriate.
It’s easy to dismiss subtle changes in the colour or consistency of your stool, but any change which lasts for more than one or two days is significant, and it’s always better to err on the side of caution.
It’s important to seek immediate medical attention if your stool is bright red, black or white, as these colours could indicate a serious medical condition.