Citric acid is a weak organic acid that has the molecular formula C₆H₈O₇. It occurs naturally in citrus fruits. In biochemistry, it is an intermediate in the citric acid cycle, which occurs in the metabolism of all aerobic organisms. More than two million tons of citric acid are manufactured every year.

Citric acid is most prevalent in citrus fruits and juices. Of these fruits, lemons and limes have the most citric acid. While oranges, grapefruits, and berries also contain appreciable amounts, lemons and limes will most significantly contribute to the citric acid content of your urine.