The most common cause of a UTI is bacteria from the bowel that live on the skin near the rectum or in the vagina which can spread and enter the urinary tract through the urethra. Once these bacteria enter the urethra they travel upwards causing infection in the bladder and sometimes other parts of the urinary tract.* 

Sexual intercourse is a common cause of urinary tract infections because the female anatomy can make women more prone to urinary tract infections. During sexual intercourse bacteria in the vaginal area is sometimes massaged into the urethra by the motion of the penis.*

Women who change sexual partners or begin having sexual intercourse more frequently may experience bladder or urinary tract infections more often than women in monogamous relationships. Although it is rare, some women get a urinary tract infection every time they have sex.*  

Another cause of bladder infections or UTI is waiting too long to urinate. The bladder is a muscle that stretches to hold urine and contracts when the urine is released. Waiting very long past the time you first feel the need to urinate causes the bladder to stretch beyond its capacity which over time can weaken the bladder muscle. When the bladder is weakened it may not empty completely and some urine is left in the bladder which may increase the risk of urinary tract infection or bladder infection.*

Other factors may also increase a woman's risk of developing UTI including pregnancy, having urinary tract infections or bladder infections as a child, having past menopause, and diabetes.*