A bladder infection, also called cystitis, is a type of urinary tract infection. Bacteria usually cause the infection. Rarely a virus may cause it. A bladder infection occurs when bacteria travel up the urethra and into the bladder.
Women are more likely to have bladder infections than men because their urethra is shorter.
The short urethra makes it easier for bacteria from the anus or genital area to reach the bladder. This can happen during such activities as wiping or sexual intercourse. Most infections of the urinary tract are caused this way. Bladder infections often occur in young women who have just become sexually active and have sexual intercourse often. Anything that blocks the flow of urine from the bladder, or causes incomplete emptying of the bladder, provides a place where bacteria can grow in the urine.