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• Posted October 28, 2022

First Sex Activates Boost in Vaginal Immune Response, Study Finds

A woman's body appears to go on high alert after she loses her virginity, a new study reports.

Specifically, her immune system ramps up activity in her vagina following her first sexual intercourse, researchers found.

However, researchers can't yet say whether these immune changes reduce or elevate a female's risk of acquiring a sexually transmitted infection.

For the study, published recently in the journal eLife, the research team compared vaginal samples collected from 95 young women in Kenya before or after they began having sexual intercourse.

They found a sharp increase in proteins that control the body's immune response within the first year after the women became sexually active. They also found that the changes weren't due to either a sexually transmitted infection (STI) or pregnancy.

Data from two other studies involving 93 young women in Belgium and 19 in the United States confirmed this observation, with those participants also experiencing an immune system spike following their first time having sexual intercourse.

But because this was an observational study, the researchers noted that they can't draw a cause-and-effect link between losing virginity and the increase in immune activity.

"The initiation of sexual activity was associated with higher levels of immune mediators, but we don't know for sure if the start of sexual activity caused the changes," said co-senior researcher Dr. Florian Hladik, a professor in the Vaccine and Infectious Disease Division at Fred Hutchinson Cancer Center in Seattle.

"Other factors associated with the timing of sex initiation, such as socioeconomic status, could have contributed to immune system changes," he said in a journal news release.

It's hard to tell how this immune activation affects a woman, the researchers added. The immune changes could help boost fertility, or they may be a protective defense against STIs.

"More research on the immune changes associated with the initiation of sexual activity may help us understand the elevated STI risk in young women," said co-senior study author Dr. Alison Roxby, an associate professor of infectious disease and global health at the University of Washington School of Medicine. "It may also help us identify new ways to prevent STIs in this vulnerable population."

More information

The Cleveland Clinic has more on vaginal health.

SOURCE: eLife, news release, Oct. 25, 2022