Answer:
The tissues of the vagina and outer urethra are affected by the lack of estrogen in the postmenopausal female. The decline in estrogen causes a thinning of the tissue as well as an alteration in the pH of the tissue. Both of these alterations can reduce the body's ability to resist infection.
Studies have shown that replacement of estrogen with vaginal estrogen cream may be one way to reduce urinary tract infections in postmenopausal women.