Why does your poo smell so bad? The 6 reasons – and when you must see a doctor | The Sun

IT’S not something we typically associate with a pleasant odour.

But when your poo smells extremely bad it’s not only unpleasant, but it can cause you to worry about your health too.

But when do you know when your foul smelling poo is just a result of what you ate last night, or something more sinister?

GP Dr Deborah Lee explains why poo smells, when to worry, and how to prevent it.


Dr Deborah says: “Human faeces – poo – consists of whatever is left over after the ingestion and digestion of food and drink. 

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“It contains partially digested and undigested food, bacteria, water and dead cells from the lining of the gastrointestinal tract.

“50 per cent of the energy from the food we ingested is still present in our faeces because bacteria, fungi and other organisms live off and obtain energy from it.

“Poo is brown in colour due to the presence of bile and the bile pigment, bilirubin.”


Dr Deborah says: “Human poo is smelly not because of the poo itself, but because of what is produced in the gastrointestinal tract during the digestive breakdown of what we eat and drink.

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“The substances produced during digestion that are responsible for foul smells include:

Skatole: The real chemical name for Skatole is 3-methylindole and it is produced when the amino acid Tryptophan, found in many foods, is broken down.

In low concentrations, this has a pleasant smell – of orange blossom and jasmine – and is even used in the perfume industry, but in large quantities, it smells very unpleasant. 

Methanethiol: This colourless gas smells of rotten cabbage. This gas is naturally produced in the bowel when foods are broken down and it is found in foods such as garlic and onions.

Hydrogen sulphide: This gas is produced when foods that contain sulphur are fermented in the bowel during digestion. This gas smells of rotten eggs and also causes smelly farts.

How to reduce smelly poos

Dr Deborah says: “There are many lifestyle changes you can make to help reduce the smell of your poo. Here are a few of the ones I recommend.”

Avoid a very high sulphur diet: “If you want to reduce your poo smell it could be worth looking at your diet and cutting down on sulphur rich foods."

  • Cruciferous vegetables – Brussels sprouts, cabbage kale, spinach, broccoli,Pak Choi, kale, radish, turnips and watercress
  • Dairy products
  • Dried fruits
  • Garlic

Avoid processed foods: "Processed foods are not only unhealthy and low in nutrients, they are also high in sugar, salt and unnatural preservatives. This also included carbonated drinks.”

Cut down on alcohol: “Alcohol wreaks havoc with your gut and the bacteria within it. Cut down your consumption or cut it out completely to help avoid smelly poos.” 

Visit your GP: "If you have long-term smelly poo or are experiencing a big change from normal that is

not settling, see your GP.
“Smelly poo can be a sign of disease and should be checked out.”


Spices in your food: Lots of spices we use to flavour our foods contribute to smellier poos. Coriander, turmeric, ginger and garlic and particularly responsible for smellier-than-normal poos due to how their smells combine with the gasses created during digestion.

High sulphur foods: The body needs fat to function, but diets that are very high in fat can cause smelly poos.

High fat diets are troublesome because the gut is unable to absorb all the fat, leaving the gut overwhelmed with fat and needing to “get rid” of it in our poo.

Poo that contains a lot of fat typically smell more due to the smell of fat being particularly unpleasant.

Acholic stools: The medical term “acholic ” simply means poos that are light and clay-colored and they occur due to a lack of bile.

These often greasy stools have an unusual and unpleasant smell and may signify liver or pancreatic disease, especially if experienced with every bowel movement. If you notice you are producing acholic stools, see your GP.

Bowel infections: Very common in humans, bowel infections are caused when ‘bugs', or germs enter the gut.

An infection of the bowel is often referred to as a gastrointestinal infection, or gastroenteritis by medical professionals. These can cause painful bowel movements, needing to poo frequently, loose, watery poos (diarrhoea) and foul smelling poos.

Alcohol Poos: You may have experienced it in the past after a night out or particularly boozy dinner party, and they are named “alcohol poos” because alcohol can result in smellier poo when we over consume it.

High levels of alcohol in the blood can affect your stomach and the intestines and alter the bacteria in your gut.

This bacterial imbalance prevents your gut from doing its job as well as usual and the result of this is foul-smelling gas and poo.
Alcohol also contains sulphate, a substance that can smell of rotten eggs when passed out of the body.

Taking antibiotics: Antibiotic medication can affect gut function as it kills off not just bad bacteria in the body, but the good bacteria in the gut too.

When the bacteria in the gut is killed off we cannot breakdown, digest or absorb food properly, resulting in foul smelling poo.

Food intolerance: Many of us suffer with intolerances to certain foods or food types.

Due to the way we reject or react to these foods impacts the smell (as well as other aspects) of our poo.

A lactose or gluten intolerance often results in diarrhoea, painful poos and smelly poos.

But while some of us know we have serious food intolerances, others might not if the symptom is only “smelly poo.”

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Speck to your GP if you think you might have a food intolerance, or try cutting out common foods to see if things change.

GP Dr Deborah Lee founded Fox Online Pharmacy.

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