It’s typical to notice some digestive fluid or mucus in your colostomy bag. The color and consistency of these fluids can vary, depending on factors like your diet. But it could also be a symptom of a medical emergency.

A stoma is a hole in your abdomen that lets stool bypass part of your gastrointestinal (GI) or urinary tract.

A colostomy is when a surgeon connects part of your large intestine to a hole in your abdomen so that stool can bypass your lower colon and collect in a colostomy bag.

Black fluid inside your colostomy bag can suggest bleeding in your GI tract. It can also have milder causes, such as:

  • pigments from your food
  • digestive fluids mixing with charcoal from your bag’s filter
  • medication side effects

This article reviews some reasons why you may develop black fluid in your colostomy bag.

Some causes of black stoma output are serious, but many aren’t a cause for concern. A medical professional can help you find the root cause.

Bleeding in the gastrointestinal tract

GI bleeding can turn your stool a tarry black color. The most common cause of GI bleeding is stomach ulcers. Blood in your GI tract can mix with mucus or digestive fluids and potentially turn them black.

GI bleeding often causes a strong, foul odor caused by the activity of digestive enzymes and bacteria on hemoglobin in your blood cells.

Medical emergency

GI bleeding is an emergency that requires prompt medical attention. Get emergency medical attention right away if you have:


Certain foods contain pigments that can change the color of your stool or digestive fluids. Black, purple, or dark blue pigments may cause your stool to appear black.

Anthocyanins are a group of pigments that give fruits and vegetables a red, purple, or blue color. These pigments are in:

  • berries
  • currants
  • grapes
  • some tropical fruits

Consuming more of these foods than usual may change the color of your stool. Ultra-processed foods with added colors, like black licorice, may also change your stool and digestive fluid color.


Some medications like iron or bismuth can cause stools and digestive fluid to appear black. Usually, this isn’t a cause for concern.

Bismuth is often in medications people take to treat GI symptoms. For example, bismuth subsalicylate is the active ingredient in Pepto-Bismol.

Particles from the filter

Many colostomy bags contain charcoal to absorb odors caused by gas released from the bag. Some people may notice black fluid coming from the vent holes if the filter gets wet. This usually isn’t a cause for concern.

Stoma necrosis or infection

Necrosis is the death of tissue around your stoma from a lack of blood flow. Some studies from a 2022 research review showed that necrosis may develop in up to 16% of people who receive stomas.

In theory, black and dead pieces of tissue may enter your colostomy bag and give the stool or fluid a black appearance.

It’s also theoretically possible for this to happen for some infections.

Your large intestines help absorb liquid from your stool. If you have a colostomy bag, your stools may be more watery than before your surgery since they bypass part of your large intestine.

Medical emergency

Passing watery stools combined with a reduction in stool volume or a complete lack of stool is a symptom of a stoma blockage. A stoma blockage is a medical emergency that requires immediate attention. Go to the nearest emergency room if you experience this along with other symptoms like:

  • nausea and vomiting
  • abdominal cramps
  • swelling or bloating

A yellow liquid in your colostomy bag may be reflective of your diet. It could also be mucus that your bowel lining produces. It’s typical for your bowel to produce some mucus, but it’s a good idea to contact a doctor if you develop other concerning symptoms.

Fluid in your colostomy bag can be different colors, depending on what you eat. For example, Some foods like beets may cause bright redness that may look like blood.

Usually, your stool will be a brown color. Fluid in your colostomy bag is often the same color as your stool since they usually mix.

Symptoms of a stoma infection include:

  • pus
  • swelling
  • redness, which may be difficult to notice on darker skin tones
  • other color changes

It’s essential to contact your doctor if you notice concerning changes to your stool or fluids collecting in your colostomy bag.

It’s critical to get immediate medical attention if you develop blockage symptoms, such as fluid collecting in your colostomy bag in the absence of stool.

Treatment for the cause of black fluid in your colostomy bag may include:

GI bleeding • medications
• endoscopic surgery
• injections
Medications• no treatment usually needed
Diet• no treatment usually needed
Infection• antibiotics or antifungals

Black fluid in your colostomy bag can be a sign of bleeding somewhere in your GI tract. GI bleeding is a medical emergency that requires prompt medical attention.

Black fluid can also have a mild cause, such as:

  • pigment from your food
  • particles from the charcoal in the filter
  • medication side effects

Usually, these causes aren’t serious, but it’s still important to consult with your healthcare team if you develop concerning changes.