There was a medical case involving a 70-year-old French woman that made headlines not long ago (after being published in the New England Journal of Medicine) because her symptoms were so unbelievable. According to Health, the patient had a urinary catheter inserted, and ten days later, it was reported that her urine had a purple discoloration to it. Interestingly, the woman showed no signs of infection. Although doctors chose to give her intravenous hydration, she was not placed on antibiotics for the condition as her medical professionals felt that it was a result of “a chemical reaction of certain bacteria in an alkaline environment.” Several days later, her urine returned to normal.

Purple urine is not normal and is considered rare. Still, according to Health, it’s also not as uncommon as people think, affecting 10 percent “of institutionalized patients who depend on a catheter long-term.” This condition was first identified in 1978 and is called Purple Urine Bag Syndrome (PUBS). Although these incidents must be alarming for patients, Fox News notes that PUBS is considered a “benign phenomenon,” and a case report from the journal Annals of Long-Term Care defined it as “as a result of a chemical reaction facilitated by certain bacteria in [an] alkaline environment.”

It is believed that PUBS’ appearance is a reaction between specific bacteria and tryptophan, Fox News reports. When tryptophan enters the gut, it is broken down into the chemical compound indole, which is then converted to indoxyl sulfate, after the liver metabolizes it. When indoxyl sulfate comes into contact with bacteria, they mix in the urinary bag, resulting in the purple color. NCIB expands on PUBS, and notes that those who are at risk for it are usually women and “chronically debilitated patients with long term indwelling urinary catheters.” It is often associated with bacterial urinary infections. The publication claims that the discoloration is due to the presence of indigo (blue) and indirubin (red) pigments, "which precipitate and react with the synthetic materials of the catheter and urinary bag."

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