A study published Wednesday found that women who practiced "extreme" grooming habits, shaving all or most of their pubic hair on a regular basis, are not at higher risk of contracting certain sexually transmitted infections, contradicting past research.

The study, published in the journal Plos One, found no correlation between pubic hair grooming and chlamydia or gonorrhea risk. Past studies, however, have found a link between grooming habits and higher rates of STIs.

The new findings come as STI rates in the U.S. continue to rise. According to the Centers for Disease Control and Prevention, STI rates have been increasing since 2013, with half of all diagnoses from 2013 to 2017 occurring in people ages 15 to 24. The most common STI, chlamydia, had 1.7 million reported cases in 2017; 45 percent of those cases occurred in women in this age group.

Given the rising rates, “it’s important to find any modifiable risk factors that we can so we can design interventions and decrease the number of people affected by STIs,” said Jamie Luster, who led the new study as a graduate student at the Ohio State University College of Public Health.

One hypothesis was that pubic hair grooming could be a risk factor for contracting an STI.

To study the link, the researchers recruited 214 women who were students at Ohio State University. The participants, who were predominantly white and single, answered a series of questions and got tested for gonorrhea and chlamydia at the university’s health clinic. The questionnaire asked whether the participants had ever groomed their pubic hair, about their hair removal methods (shaving with a nonelectric razor was the most common), how often they groomed and how much they removed when they do.

More than half of the women identified as “extreme” groomers, meaning they had chosen to go hairless on at least a weekly basis within the past year. Almost 40 percent said they were extreme groomers within the past month and nearly all of the women reported at least some grooming in their lifetime as well as having had sex at least once. In contrast to the high rates of going hairless, less than 10 percent of participants tested positive for either chlamydia or gonorrhea and no one tested positive for both.

Because only 10 percent had chlamydia or gonorrhea but most reported grooming, the researchers concluded there was no link between how often a woman grooms and her risk of contracting the two most common STIs.

Levels of sexual activity, on the other hand, were more closely tied to extreme grooming, the researchers found: Forty percent of the extreme groomers reported having sex on a daily or weekly basis in the past year.

“Sexual frequency ... could be related to how often they groom,” said Luster, who is now a researcher at Michigan Medicine.

Asking about sexual activity is important, according to Debby Herbenick, a professor of public health at Indiana University and author of "Sex Made Easy." When it comes to risk factors for STIs, “we’re sometimes barking up the wrong tree with the focus on pubic hair, especially if researchers haven’t asked the right questions around sexuality,” Herbenick, who wasn’t involved with the new research, told NBC News.

A 2016 study published in the journal Sexually Transmitted Infections was one of several that linked frequent pubic hair grooming to higher rates of STIs. Researchers at the University of California, San Francisco, surveyed more than 7,500 men and women between18 and 65. Participants reported their lifetime grooming habits, sexual behaviors and STI history. The study found that people who had undergone a below-the-belt haircut at least once in their lifetimes were almost twice as likely to have contracted at least one STI. People who groomed weekly and those who took it all off more than 11 times a year were more than three and four times as likely to have had an infection, respectively.

“Part of the challenge with this whole body of literature is that we can identify an association, but it’s very difficult to imply causation,” said Dr. E. Charles Osterberg, an assistant professor of surgery at the University of Texas Dell Medical School in Austin, who co-authored the 2016 study.

One possible link between grooming and STIs is that the actual grooming itself could cause microtears that make it easier for bacteria and viruses to get into the body, Osterberg said. Waxing and shaving could also irritate the skin and trigger an HPV, or genital wart, outbreak in a person who already has the virus.

Still, Luster and Osterberg said their studies were not conclusive, but rather add to the growing body of data. They agreed that further research that includes elements from both of their studies — such as racial and ethnic diversity that reflect the population, including all genders, and providing on-site STI testing that’s compared to current grooming habits — is still needed.

“We really have just scratched the tip of the iceberg,” Osterberg said. “If there is some association here, we could be doing tremendous due diligence in public awareness.”

Whether down-there grooming has anything to do with it, one thing is clear: STIs are becoming more common. Gonorrhea rates hit historic lows in the U.S. in 2009, but have increased by more than 75 percent since then, CDC data shows. The jump is particularly concerning due to the rise in antibiotic-resistant strains of the bacteria, but gonorrhea’s comeback isn’t an outlier.

Reported cases of syphilis, which has been on the decline since the early 1940s, nearly doubled from 2013 to 2017, and chlamydia diagnoses remain at record highs. Herbenick said that although multiple factors are fueling the spike, falling condom use significantly increases the risk of STIs, and the popularity of long-acting forms of birth control could be to blame.

“These have been fantastic in preventing unintended pregnancies, but they offer no protection against STIs, and people aren’t using condoms as often when they are using these other forms of birth control,” Herbenick said. “We need people to use condoms when they have sex if we want to see a decrease in STIs.”

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