Your urinary tract is the system that makes urine and carries it out of your body. It includes your bladder and kidneys and the tubes that connect them. When germs get into this system, they can cause an infection.
Urinary tract infections typically occur when bacteria enter the urinary tract through the urethra and begin to multiply in the bladder. Although the urinary system is designed to keep out such microscopic invaders, these defenses sometimes fail. When that happens, bacteria may take hold and grow into a full-blown infection in the urinary tract.