People who prune their pubic hair are up to four times more likely to have had an STI at some point in their lives, a new study finds.

A survey of 7,580 people between 18 and 65 years old in the US has shown that removing or trimming pubic hair is linked to heightened risk of contracting STIs compared with doing no pubic-hair grooming, according to a study published in the BMJ.

What's the risk?

On average, people who trimmed or removed hair were 80% more likely to have had an STI at least once in their lives. The more extreme the hair removal, the greater the risk, the study found. The most extreme groomers were up to four times more likely to get an STI.

The study asked respondents whether they had ever had one or more of: herpes, human papillomavirus, syphilis, molluscum, gonorrhoea, chlamydia, HIV or pubic lice.

The study took into account the number of sexual partners people had had, to make sure that the results weren't skewed by the amount of sex they had.

The increased risk associated with grooming was most pronounced for infections that require skin-to-skin contact, such as herpes and HIV.

However, those who did not groom faced other problems – low-intensity groomers had double the risk of pubic lice infestation.

Are you extreme?

'Extreme groomers' were defined as people who remove all pubic hair at least 11 times a year (17% of groomers). 'High-frequency groomers' were people who attended to their pubic hair daily or weekly (22% of groomers). Both categories were associated with increased risk of getting an STI.

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Shaving pubic hair was linked to a greater incidence of STIs. iStock

Almost three-quarters of survey respondents said that they trimmed or removed hair at least once a year. The figure was 84% for women and 66% for men.

Overall 13% of respondents reported having an STI at least once in their lives.

What's the cause?

One possible mechanism that the authors propose for the link is that tiny tears in the skin after grooming may make it easier for viruses and bacteria to enter and cause an infection. However, it could be that there is an entirely independent factor that links grooming and increased risk of STI that is the cause, they note.

Claudia Estcourt of the British Association of Sexual Health & HIV (BASHH), who was not involved with the study, told IBTimes UK that the association could be because people who groomed more often also tended to have riskier sexual practices, which increased their risk of getting an STI, as the authors acknowledged in the paper.

"It could just be that people who are more risky sexually also tend to groom more. So it's just two things that go together," Estcourt says.

In general, riskier sexual behaviour includes not wearing a condom and certain types of sex. For example, anal sex carries a higher risk of transmitting an infection than vaginal sex. Having a greater number of sexual partners also counts as riskier behaviour, but the study authors controlled for this in the study, making it unlikely to be a common factor causing both increased likelihood of getting an STI and increased likelihood of shaving.

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More than half of both men and women groom their pubic hair. Phuket photographer / Flickr

It may not be hair removal that triggers STIs but the reverse, the authors note. It's possible that people may become more likely to remove hair after getting an STI.

"It's a very scientifically rigorously conducted study," says Estcourt. "They've been very clear when they discuss the findings in the article to say what they see as an association and what might be causal."

"The media has driven adoption of new grooming patterns and modern society's definition of attractiveness, cleanliness and feelings of femininity or masculinity. As a result, our perception of genital normalcy has changed," the authors write in the paper.

So should you stop waxing or shaving?

This study alone isn't enough to say that waxing, shaving or otherwise pruning your pubic hair directly makes you more likely to get an STI. There could be other factors that explain the association.

If grooming is indeed the direct cause of increased risk of getting an STI, then the authors say that delaying sex until hair has begun to grow back could be one strategy to lower the risk of infection. The study authors say that more research needs to be done to find out more about the link between STIs and pubic hair grooming before any concrete advice can be given.