If your poop is much lighter colored than nearly everyone else’s, it could be a sign that you have an absolutely harmless medical condition. And your parents are to blame.

Three to seven percent of Americans have Gilbert syndrome. The syndrome is caused by a mutation on the UGT1A1 gene—specifically a mutation on the promoter region of the gene. The promoter region of the gene is a sequence that starts the process by which the genetic code is read, transcripted, and expressed as proteins. The trait is recessive. For a person to actually have the syndrome, they have to have inherited a faulty gene from both their mother and their father.

Gilbert syndrome causes one enzyme in the liver to only function at a third of its normal capacity. This specific enzyme breaks up a chemical called bilirubin, which is made from broken-down blood cells. The form of bilirubin that flows into the liver cannot be removed from the body. The enzyme goes to work on it, adding an acid, after which bilirubin takes on a form that dissolves in water, and can be excreted with no problem. When the body can’t convert bilirubin into a water-soluble form, it builds up in the blood. At first, this causes jaundice, a condition in which the skin and eyes to take on a yellowish cast. After a while, the build-up can be toxic.

Jaundice is seen in people going into liver failure, and in babies whose livers haven’t yet “come online.” The babies are monitored, but usually require little care. People with liver failure often need new livers. People with Gilbert syndrome generally need nothing at all. Sometimes their blood bilirubin levels are slightly elevated, but it rarely becomes a problem.

There is one major symptom, though. Bilirubin is a yellow-brown color. When it’s excreted, it’s excreted through feces. In fact, it’s the main coloring agent in feces. Enough bilirubin turns poop brown. When something stops bilirubin from getting excreted, poop is a yellow to light tan color. Since someone with Gilbert syndrome is generally not processing the same amount of bilirubin a normal person is, and since Gilbert syndrome is hereditary, pooping yellow or tan is an inherited trait.

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Image: Brandon Blinkenberg