In recent years, researchers have also been investigating what your feces can reveal about the bacteria that reside in your gut, and how it can affect many aspects of your mental and physical well-being. For example, the so-called gut microbiome may play a role in mood disorders, according to a study published in August 2015 in Brain, Behavior, and Immunity. The mysterious microbes could even be a factor in the development of Alzheimer’s, as a recent study on mice published in Nature in February 2017 suggests. While you may not have the scientific tools to examine your poop’s bacterial composition, you can still learn a lot from its appearance. Read up on the meaning behind the many different shades of stool.

Brown

Poop owes its normal, brown color to bile, a substance produced by our liver that helps us digest fats, says Dr. Nandi. (Though bile is naturally green, its pigments change color to yellow and brown as they travel through your digestive system and are broken down by enzymes.) If your excrement is brown and solid, you have no obvious reason for concern.

Green

Green poop is “very much in the realm of normal,” says Arun Swaminath, MD, director of the inflammatory bowel diseases program at Lenox Hill Hospital in New York City. It is usually attributed to something you ate, adds Nandi. Eating lots of green, leafy vegetables like spinach or kale — rich in the pigment chlorophyll — will easily give your feces an emerald hue.

White

Whitish, clay-colored poop is caused by a lack of bile, which can stem from a blockage of bile ducts. Gallstones are one possible culprit of such an obstruction, says Dr. Swaminath. In addition, “Sometimes people can see white mucus on top of normal colored stool which has a whitish coating,” he says. This can be normal or a sign of a Crohn’s flare. Crohn’s disease causes ulcers in the intestines, which produce mucus in the stool. Alert your doctor when you notice mucus in your bowel movements, especially if it’s more than usual.

For people without Crohn’s, white poop along with abdominal pain, fever, or vomiting means they should call the emergency services. But if you see white poop without any of the aforementioned symptoms, you can wait to see a doctor, Swaminath says.

Yellow

Yellow poop is another potential indicator of bile shortage, which, again, may be related to obstructed bile ducts. It can also mean that the pancreas is not secreting enough enzymes needed for digestion. “Oftentimes, a few questions about one’s health and medical history by a medical professional can suggest the underlying reason with tailored testing to confirm the diagnosis,” says Nandi. But these aren’t the only possible explanations. When people prep for a colonoscopy, their stool becomes diluted and can also turn yellow, says Nandi. This is a normal phenomenon that shouldn’t cause any concern.

Black

If you have ever taken iron tablets or Pepto-Bismol, you have likely experienced this common, though harmless, side effect: black poop. Indeed, certain ingredients in some foods or medications are the most common reason behind your stool turning dark. Even eating a full pack of Oreos can have this effect, says Nandi. If your poop is dark and solid, you probably have nothing to worry about. But black poop with a more liquid, tarry consistency and a particularly pungent smell is a sign of bleeding in the gastrointestinal system. This issue “may require emergency evaluation with endoscopy,” says Swaminath.

Bright red

Bright-red stool often results from consumption of scarlet-colored foods or drinks like beets or tomato juice, but it might also indicate bleeding. Small amounts of blood in the stool may be from hemorrhoids, colon polyps, or anal fissures, especially if you are also experiencing pain when pooping, says Swaminath. “Larger amounts of bleeding require hospital admission and further evaluation, often with colonoscopy, to identify and treat the source of bleeding,” he says.

One of the hallmark symptoms of inflammatory bowel diseases like Crohn’s disease is bloody diarrhea. Although this is a common symptom of the disease, it’s not normal, and you should tell your doctor how much blood is present in your stool.