The bacteria living inside women in the United States and China are so different that a single standard for vaginal health may not work for both populations. A new study published in the journal Med shows that Chinese women carry a much higher proportion of a bacterium called Lactobacillus iners, while American women are more likely to host Lactobacillus crispatus. The finding upends the common assumption that a healthy vagina looks the same everywhere.
Why a single health standard may not fit all women
Researchers from China and the United States analyzed vaginal swabs from 1,600 women across both countries. They found that the microbial makeup of Chinese women was dominated by Lactobacillus iners, a species that produces less lactic acid than its cousin Lactobacillus crispatus. Lactic acid helps keep the vagina acidic and hostile to harmful bacteria. In American women, Lactobacillus crispatus was far more common, creating a more acidic environment overall.
The study also looked at the vaginal microbiomes of women in South Africa and Kenya. Those populations showed yet another pattern, with higher levels of bacteria from the genus Gardnerella, which is often linked to bacterial vaginosis. The researchers concluded that ethnicity, diet, hygiene practices, and sexual behavior all shape the vaginal microbiome in ways that vary by region.
What this means for diagnosis and treatment
Doctors in China and the United States currently use the same criteria to diagnose bacterial vaginosis, a common infection linked to preterm birth and HIV risk. But those criteria were developed mostly based on data from Western women. The study suggests that applying them to Chinese women could lead to misdiagnosis, because what looks like an imbalance in one population may be normal in another.
For example, the Nugent score, a standard lab test for bacterial vaginosis, may flag a Chinese woman as having an infection when her microbiome is simply typical for her region. The researchers call for region specific guidelines that account for these differences. They also note that probiotics and treatments developed in one country may not work as intended in another.
A call for more diverse medical research
The study was led by scientists at the Chinese Academy of Sciences and the University of California, San Diego. They argue that medical research has long been skewed toward Western populations, and that this bias can lead to ineffective or even harmful treatments for people in other parts of the world. The vaginal microbiome is just one example of a broader problem.
Local doctors in China have already begun to question whether imported health standards apply to their patients. The study gives them data to back up those concerns. It also opens the door to developing diagnostics and treatments tailored to the microbiomes of Chinese women, rather than relying on a one size fits all model imported from abroad.
