Why is my stool green?

Noticing a change in your stool colour can be alarming, and green poop is no exception. While a green hue may sound concerning, it often reflects harmless factors such as diet or mild changes in digestion. In some cases, however, green stools can signal an underlying issue that needs attention. This article explores why poop can appear green, the most common causes, when it is nothing to worry about and when you should seek advice from a healthcare professional.

What determines stool colour
Normal stool colour ranges from golden to brown, primarily due to a substance called bilirubin. This pigment originates from the breakdown of red blood cells and is processed by the liver, then secreted into the gut as part of bile. As bile travels through the intestines it transforms from green to brown as bacteria modify its chemical structure. Thus the speed at which stool moves through the gut and the foods or medicines you consume both influence its ultimate shade.

Dietary factors
One of the simplest explanations for green poop is the consumption of certain foods. Leafy green vegetables such as spinach, kale and broccoli contain chlorophyll, the green pigment that colours their leaves. Eating large quantities of these vegetables can pass enough chlorophyll through your system to tint your stool. Likewise, foods or drinks with artificial green or blue food colouring found in sweets, popsicles or sports drinks can result in a green appearance. Simply reducing or spacing out these items usually returns stool to its normal hue.

Bile pigment and rapid transit
Bile starts off as a green fluid. As it mixes with digestive enzymes and passes through the small and large intestines, bacteria break it down and change its colour to brown. If food moves too quickly through the digestive tract, there is less time for this transformation. Conditions that speed up transit time, such as mild diarrhoea after a stomach bug or a week of stress, can lead to green stool because the bile has not been fully processed. Once gut motility slows back to normal, stool typically returns to its usual brown.

Antibiotics and other medications
Medications that alter gut flora can affect stool colour. Antibiotics in particular may reduce populations of bacteria responsible for breaking down bile. When these bacteria are suppressed, bile remains green and passes through the colon unchanged. Other medications, such as iron supplements or certain laxatives, can also change stool colour. If you start a new treatment and notice a green tint, check the patient information leaflet and ask your GP or pharmacist whether it could be a side effect.

Supplements and herbal remedies
Some herbal supplements and health products contain large amounts of green plant extracts. Chlorella, spirulina and wheatgrass powders are popular for their nutritional benefits but are potent sources of chlorophyll. Taking concentrated doses of these supplements can easily tint your stool until your body adjusts or you stop taking them. If you suspect a supplement is responsible, try pausing use for a few days to see if the colour normalises.

Infections and gut inflammation
While diet and medications are the most common reasons for green stool, certain infections can play a role. Bacterial infections such as salmonella or giardia can cause rapid transit and diarrhoea, leading to green stool. Viral gastroenteritis also speeds up gut motility. In these cases, green stool is accompanied by other symptoms such as abdominal cramps, nausea, fever and dehydration. If green diarrhoea persists for more than twenty four hours or becomes severe, you should seek medical advice.

Irritable bowel syndrome and other chronic conditions
Irritable bowel syndrome (IBS) can affect stool consistency and transit time, leading to periods of diarrhoea with green stools. People with IBS often experience alternating constipation and diarrhoea, as well as bloating and abdominal pain. Inflammatory bowel diseases such as Crohn’s disease or ulcerative colitis may also cause changes in stool colour due to inflammation of the gut lining and altered digestion. These conditions usually present with additional signs such as weight loss, blood in the stool or fatigue and require specialist care.

Newborns and babies
Green stool is common in breastfed infants during the first few days of life, when they pass meconium and transitional stools. As their digestion settles and they adapt to breastfeeding, stool colour shifts to yellow. If green stool continues beyond the first week, it may signal oversupply of foremilk over hindmilk, causing diarrhoea. Adjusting feeding patterns can help restore a healthy balance. Formula fed babies may also pass green stools if they react to certain ingredients. Paediatric advice should be sought if there are concerns about hydration or growth.

When to seek medical advice
Most episodes of green stool are harmless and resolve within a couple of days. However, you should contact your GP or NHS 111 if you experience:

• Persistent green diarrhoea lasting more than twenty four hours.
• Signs of dehydration such as dark urine, dizziness or rapid heartbeat.
• Severe abdominal pain, fever or chills.
• Blood or black tarry markings in your stool.
• Unexplained weight loss or fatigue.

Early assessment helps rule out serious infections or chronic digestive diseases and ensures prompt treatment if needed.

Home care strategies
If green stool arises from mild transit changes or diet, simple self‑care often suffices. Drink plenty of fluids to prevent dehydration, especially if you have diarrhoea. Consume bland foods such as rice, bananas and toast to firm stool. Probiotics or yoghurt with live cultures can help restore healthy gut bacteria. Resume your normal diet gradually, reducing foods with strong green pigments until your stool colour normalises.

Common myths and misconceptions
A frequent myth is that green stool always indicates a serious problem. In reality, diet and mild changes in gut motility are far more common causes. Another misconception is that you should avoid all green foods if you see green stool. These foods offer valuable nutrients, so rather than eliminating them, enjoy them in moderation and alongside a balanced diet. Finally, some believe that green stool means poor digestion. While rapid transit is a factor, the colour alone does not necessarily reflect long‑term digestive health.

Emotional and mental impact
Changes in stool colour can cause anxiety and embarrassment. Discussing bowel habits openly with your GP can relieve worry and clarify when green stool is benign. Remember that healthcare professionals treat digestive questions routinely and maintain strict confidentiality. Keeping a simple food and symptom diary can help you and your doctor identify patterns without unnecessary stress.

Summary
Green stool is usually the result of dietary factors, rapid transit of bile or temporary disruptions to gut flora from illness or medication. In most healthy adults it is a harmless and temporary change. Persistent green diarrhoea, severe symptoms or additional warning signs warrant medical attention to exclude infection or chronic conditions. By monitoring your diet, staying hydrated and seeking advice when needed, you can manage green stool with confidence and maintain digestive health.