The opening of the urethra is at the vagina in women. When this happens, the bacteria cause infection and inflammation of the bladder. In other words, they multiply, causing irritation, swelling, and pain. Bladder infection, also called cystitis, is the most common urinary tract infection. If the bacteria travel upward from the bladder through the ureters and reach the kidneys, you may develop a kidney infection, also known as pyelonephritis.
Kidney infections are much less common but often more serious than bladder infections.
When you have a urinary tract infection, the lining of the bladder and urethra becomes irritated just as the inside of your nose or throat does when you have a cold. The irritation can cause pain in your abdomen and pelvic area and may make you feel the need to constantly empty your bladder. In addition, you may feel a burning sensation as the urine comes out. You may notice that the urine has an unpleasant odor or a cloudy look. At times, bladder infections may also cause low back pain, fever, or chills.