First, the good news: Sex does not cause bladder infections. Symptomatic bacterial invasion of the bladder is responsible for this common, painful infection. Now for the bad news: Sex -- vaginal intercourse, in particular -- increases a woman's risk for a bladder infection by potentially helping bacteria gain entry into the bladder. Many other factors also influence bladder infection risk, including characteristics of the invading bacteria, age and personal circumstances and choices related to a woman's sex life.
The Link Between Sex and Bladder Infections
The link between sex and bladder infections in women boils down to anatomy and proximity. Most bacteria responsible for female bladder infections normally inhabit the colon. Due to the passage of stool, these bacteria commonly live harmlessly on skin of the anal and genital region. In women, this colonization may include the opening of the vagina and urethra -- the tube through which urine passes out of the body. As the vagina lies just behind the urethra, thrusting motion within the vagina during sex can push bacteria from the urethra into the bladder. The urethra is only 1.5 to 2.0 inches long in women, compared to roughly 8.5 inches in men. Therefore, bacteria have little distance to travel to gain entry into a woman's bladder.
The risk for bladder infection, also known as cystitis, increases along with the frequency of intercourse among both young and postmenopausal women. A hallmark study, published in August 1996 in "The New England Journal of Medicine," evaluated sexual and contraceptive risk factors for bladder infections among nearly 800 healthy women aged 18 to 40 who were not pregnant. The researchers confirmed that a premenopausal woman's bladder infection risk significantly increases in proportion to the number of times she has intercourse weekly. For example, the study found that a woman who has intercourse 4 times per week has roughly 3.5 times the risk of developing a bladder infection, compared to a woman who has sex once weekly.
A separate study, reported in the May 2004 edition of "JAMA Internal Medicine," evaluated bladder infection risk factors among more than 1,800 postmenopausal women aged 55 to 75. The researchers found that women who had intercourse at least once weekly had an increased risk for cystitis, compared to those who had sex less frequently or were not sexually active.
Contraceptive Choices Influence Risk
Contraceptive choices can influence a woman's risk of developing a bladder infection. Specifically, use of contraceptives that require or include a spermicide increases the risk. The study published in 1996 in "The New England Journal of Medicine" definitively established that participants who used a diaphragm with a spermicide had an increased risk for bladder infections. The researchers also noted a possible association between cervical cap with spermicide use and increased bladder infection risk, but this finding was not conclusive. However, a study published in June 2000 in the "American Journal of Epidemiology" found that both diaphragm and cervical cap users had an increased risk for recurrent bladder infections.
Additionally, women whose partners use spermicide-coated condoms have an increased risk for cystitis, as reported in studies published in the September 1996 issue of the "American Journal of Epidemiology" and the July 2002 edition of "Epidemiology." Spermicides are believed to increase bladder infection risk by promoting growth of infection-causing bacteria on a woman's genital skin and urethral opening.
The Partner Question
Given the link between intercourse and cystitis risk, researchers have examined the potential role of a woman's sex partners. The June 2000 "American Journal of Epidemiology" study report noted that young women with their first bladder infection who took on a new sex partner within the 6-month study period had an increased risk for another case of cystitis. A second study, published in October 2000 in "The Journal of Infectious Disease," similarly found that a new sex partner within the past year increased the risk for a recurrent urinary tract infection in young women. Exposure to new bacteria that might cause a bladder infection is believed to account for the increased risk associated with having a new sex partner.
What's a Woman to Do?
Unfortunately, there is no guaranteed way to avoid getting a bladder infection -- whether related to sexual activity or not. However, there are steps women can take to reduce their risk of developing cystitis associated with intercourse. For example, avoiding use of spermicides reduces bladder infection risk, especially among women who experience recurrent cystitis. Emptying your bladder before and after intercourse might reduce bladder infection risk, although this has not been proved conclusively. Drinking cranberry juice to reduce the risk of urinary tract infections has been more broadly studied, but results have been conflicting. An analysis of studies examining this question concluded there is no clear evidence of benefit, as reported in October 2012 by the "Cochrane Database of Systematic Reviews." However, because there remains a possibility of benefit and virtually no downside, some doctors still recommend cranberry juice as a preventive measure for women who experience frequent bladder infections.
Next Steps, Warnings and Precautions
Antibiotic therapy is the only proven treatment for a bladder infection, so call your healthcare provider if you develop typical symptoms, including a frequent, urgent need to urinate and burning pain when urinating. These symptoms typically develop within 24 to 48 hours after sex, if intercourse is the precipitating factor responsible for the bladder infection. Rapid medical evaluation and treatment is particularly important for women who are pregnant or have diabetes. Fever, chills and back pain also increase the urgency of treatment, as these signs and symptoms might indicate spread of the infection to the kidneys.
If you experience frequent bladder infections, your doctor might recommend testing to check for urinary or reproductive tract abnormalities or other problems that could contribute to recurring cystitis. In some cases, prolonged low-dose antibiotic treatment or taking an antibiotic after intercourse is recommended to prevent recurrent bladder infections.
Reviewed by: Mary D. Daley, M.D.