This Week in Sex is a regular summary of news and research related to sexual behavior, sexuality education, contraception, STIs, and more.

Study: No Difference in Teen Sex Based on HPV Vaccine Promotion

A new study adds to the large body of research that should quiet anyone who is still pulling out the tired, old argument that vaccinating young people against a sexually transmitted infection (STI) will encourage them to have more sex. This time, researchers looked at state laws that promote the human papillomavirus (HPV) vaccine and found that these laws did not change young people’s behavior, despite myths that getting immunized would lead to teen sex and promiscuity.

For the study, Harvard researchers examined data from the Youth Risk Behavior Surveillance study, which has been conducted by the Centers for Disease Control and Prevention (CDC) every two years since 1991; it surveys high school students about myriad risk behaviors including drug use, having unprotected sex, or not wearing a seatbelt. The CDC recommends that all young people be vaccinated for HPV beginning at age 11, but vaccine rates lag behind those for other preventable illnesses such as measles due to the stigma attached to STIs.

The researchers compared students in states with laws promoting the HPV vaccine to their peers in other states and, in those states that had laws, they compared the behavior of students who were in high school before the law took effect to those who came after.

The findings: The proportion of students having sex in states with HPV legislation was similar to those in states without it. Teens in places with these laws are no more likely to take sexual risks (such as sex without a condom) than their peers in other states. As for the trends over time, the rate of teen sex has been going down in all states since 2007 when the HPV vaccine became widely available.

The authors conclude that HPV legislation does not appear to have a detrimental effect on teens’ sexual behavior and believe that these results should be used in conjunction with other existing research to support the introduction of these laws.

Currently, 23 states and the District of Columbia have enacted laws designed to increase vaccination rates either by requiring HPV education in school, mandating the vaccine for school attendance, or requiring insurers to offer free or low-cost shots.

These laws have been controversial over the years. Former Texas Gov. Rick Perry (R) was the first in the nation to mandate HPV vaccines but was forced to reverse his position on the shots when it was used against him during his unsuccessful bid at the 2012 Republican presidential nomination. According to this new study, however, his opponents were wrong to suggest that the HPV vaccine would encourage promiscuity.

Since HPV is the cause of most cases of cervical cancer and other types of the disease, This Week in Sex thinks that states should do all that they can to promote increased uptake of this cancer-prevention method. And other research backs this up; a study from a few years ago found that states with lower HPV vaccination had higher rates of cervical cancer.

Yes, There Is a Flesh-Eating STI, but …

Earlier this month, the Lancashire Post newspaper in England described a woman’s condition as a rare flesh-eating STI. While this made for attention-grabbing headlines about erupting genitals, it may have elicited more fear (and disgust) than necessary.

A young woman in Southport, England, was diagnosed with donovanosis, also called granuloma inguinale. Donovanosis causes painless sores or ulcers on the genitals or perineum that spread slowly. These sores have a lot of blood vessels in them, causing them to appear “beefy red,” and often start to bleed. If left untreated, the sores can infect the pelvis, abdominal organs, bones, and mouth, which can then lead to genital damage or possibly permanent scarring. People with this STI may also develop uncomfortable and itchy granulomas under the skin.

But this is not necrotizing fasciitis, the dreaded flesh-eating bacterial infection that can infect the genitals. Necrotizing fasciitis moves fast, destroying skin and tissue as it spreads. People lose body parts and even die within days.

On the other hand, donovanosis can be treated with some common antibiotics. Treatment may last a few weeks or even months, and recurrences within the first 18 months are likely.

There are only about 100 cases of this STI in the United States each year, and it is also rare in the United Kingdom. It is more common in India, Papua New Guinea, the Caribbean, central Australia, and southern Africa.

While the Post got it wrong, we all would like to avoid bloody lesions on our genitals. As always, the best way to prevent this STI is to use a condom every time you have sex.

Other People Aren’t Having as Much Sex as You Think

We’re not sure if this is good news or bad news, but we thought you should know that the people around you are not having as much sex as you think they’re having.

Since 2012, Ipsos, a European polling and marketing firm, has been surveying people around the world to determine the difference between common perceptions and reality. As part of this project, the company recently asked people in the United States and Britain how often they thought people ages 18 to 29 had sex in the last four weeks.

Apparently, we all overestimate.

People in both locations guessed that young men had sex 14 times the previous month. This would mean they were doing it 170 times a year or about every other day. Nope. Young men have sex an average of four times a month or just fewer than 50 times a year.

The estimates were even more skewed for women. Men believed that women had sex 22 or 23 times a month; the researchers pointed out that women would be doing it every weekday plus some. Again, no. Women ages 18-29 have sex about five times a month. And it’s notable that women’s estimates of how much other women were having sex were basically half of men’s. Wishful thinking from the guys?

We seem to be somewhat more on target when guessing the number of sex partners our fellow countrymen had by age 54. Britons guessed 17 for males and females, a guess that was spot on for men. Americans guessed 20 for both men and women. That number was just off by one for U.S. men, who clocked in at 19. But the overestimates were back when it came to women’s partners. The average number was just 12 in the United States, and with eight partners in the Britain, our friends across the ocean were even further off base.

These and other results will published in a book called the Perils of Perception: Why We’re Wrong about Nearly Everything, out in early September.