Why is urine sterile?

Urine is considered sterile when it is produced in the kidneys, as it is formed from the filtration of blood and does not typically contain bacteria or other microorganisms. The urinary tract, including the kidneys and bladder, has natural defenses that help prevent infection. However, once urine leaves the body, it can become contaminated with bacteria from the skin or the environment. Thus, while urine is sterile in the bladder, it may not remain so after it exits the body.