UTIs and Periods: Why Does Menstruation Influence UTI risk?

Higher vaginal pH during menstruation could increase the risk of UTIs in this window by impacting the vaginal microbiome.

Typically, vagina pH is low (acidic), between 4 and 5. The acidic pH is maintained by the presence of lactobacilli bacteria that release lactic acid and hydrogen peroxide, and by cells in the vaginal epithelium that release lactic acid when high levels of estrogen are present. As blood (pH 7.35–7.45) and tissue from the uterus travels through the vagina, the vagina becomes much less acidic. The elevated pH creates a better environment for growth of potentially pathogenic bacteria that can travel to the urinary tract from the vagina and either cause a UTI or increase UTI susceptibility. These bacteria are normally kept in check by the acidic environment.

Hormonal changes may also play a role. We know that reduced estrogen production can increase UTI risk indirectly by impacting the vaginal microbiome. Perhaps that is happening within the menstrual cycle as well. Estrogen production drops in advance of menstruation, leading to the shedding of the lining of the uterus. As mentioned above, this drop in estrogen may leave the vaginal microbiome temporarily more vulnerable.

The increase of fluid in the area may also spike the risk for UTI during menses. Increased moisture makes it easier for bacteria to grow and to move around. Bacteria can live on and travel through absorbent material used in feminine hygiene products. One study evaluating hygiene / behavior and UTI risk did find that menstruation had a strong correlation with UTI occurrence. Within the group, they observed that the subjects who changed menstrual absorbent less frequently had significantly more UTIs⁽¹⁾. With more time, the bacteria may have more opportunity to populate and travel to the urinary tract.

Another biological change during menstruation has only recently been identified: the urinary microbiome. The urinary microbiome is the complex ecosystem of microbes living in the urinary tract. While it has been established that the vaginal microbiome undergoes change during the menstrual cycle, the urinary microbiome does as well, which likely plays an important role in UTI risk.

In March 2020, researchers at Loyola University Chicago, UC San Diego, and UCLA demonstrated the variability of the urinary microbiome following both menstruation and vaginal intercourse⁽²⁾. The researchers used RNA sequencing and enhanced quantitative urine culture (EQUC) to identify the organisms in the urinary tract and their relative abundance. While measurable changes to the urinary microbiome were found in all subjects, the changes were individualized and unique to each person.

The researchers did find higher than normal levels of common skin bacteria in the urinary microbiome during menstruation. One possible explanation is the use of feminine hygiene products during menstruation that could introduce these bacteria into the area from the surrounding skin.

A 2013 review, which came out before either of the previously referenced studies, evaluated evidence from 14 different papers on the health effects of menstruation and did not find a strong association between menstruation and UTIs⁽³⁾. However, this is a difficult topic to research in a controlled way, and when that is the case, anecdotal evidence should be taken seriously. Sufferers of chronic UTIs understand their own symptoms and can recognize these patterns when they emerge. While the exact cause of the increase in UTIs during menses in some women has not been proven, we do know that changes are occurring that could very well have an impact.

Based on these collective findings, there may be some proactive actions someone can take to try and reduce the risk of UTIs during menstruation. These suggestions have not been evaluated directly and are merely speculative.

1. Probiotics. Vaginal probiotics are often recommended to be taken alongside antibiotics for UTIs and to help reduce or mitigate bacterial vaginosis, a known risk factor for UTIs. These probiotics contain lactobacilli, which research has shown can help re-establish an acidic vaginal pH. Taking a vaginal probiotic during and after menses may help restore healthy vaginal bacteria more quickly.
2. Proper menstrual hygiene. Frequent changing of absorbent feminine hygiene products, if used at all, could be helpful in reducing the risk of vaginal bacteria traveling to the urinary tract. As the research on microbiomes points out, however, these should be applied with care, as they may introduce more bacteria from the surrounding skin. Perhaps the use of a menstrual cup, which is inserted inside the vagina to catch the menstrual fluid and therefore reduce bacterial spread in the area, may be helpful.
3. Decreased sexual activity. Since sexual activity can cause further disruption of the vaginal and urinary microbiomes during this sensitive period, it may be beneficial to limit sexual activity during menstruation.

Clearly, more conclusive research needs to be done here. While we can say there seems to be a strong correlation between menstruation and UTI occurrence or UTI symptoms for women with recurrent UTIs, additional research is warranted. Hopefully, as the urinary health space continues to grow with quality research, this apparent correlation can be better understood with applied science.