A new study suggests that today’s teenagers may have less protection against genital herpes than previous generations when they become sexually active, which could lead to an increase in cases of sexually transmitted herpes as well as mother-to-child transmission.

The study, published in the Journal of Infectious Diseases, looked at two groups of teenagers—those who were 14 to 19 years old between 2005 and 2010, and those who were the same ages between 1999 and 2004. It found that fewer teens in the more recent group (30 percent) had antibodies to HSV-1, one of the two strains of the herpes virus that can cause genital infections, compared to the older group of teens (39 percent). This could leave them more vulnerable to infection.

For many years, it was thought that HSV-1 caused oral herpes infections, which most often presents as cold sores on the lips, and that genital infections were caused by HSV-2. As Dr. William Schaffner, who was not involved in the study, explained to LiveScience, he was taught that HSV-1 caused symptoms above the waist and HSV-2 was the culprit if the infection was below the waist. However, that has changed over time, possibly as a result of an increase in oral sex. In fact, the researchers noted that one study suggested as many as 60 percent of genital herpes cases were caused by HSV-1. As Schaffner put it, “HSV-1 is now having the opportunity to cause more and more herpes in the genital area.”

This may be particularly problematic for today’s teens because, as the new study suggests, they have not built up any protection to this virus as a result of better, more hygienic living conditions. HSV-1 is transmitted through saliva and skin-to-skin contact. Researchers think that in the past young people were exposed to the virus as kids and therefore able to build up antibodies that could protect them if they were exposed to it again once they became sexually active. The researchers believe that the lack of antibodies coupled with the increase in oral sex is a recipe for more genital herpes infections in the future.

Genital herpes infections—whether caused by HSV-1 or HSV-2—can lead to painful sores on the penis, vulva, or anus. While some people get these sores only once, for others outbursts can recur regularly. There is no cure for herpes, though anti-viral medication can reduce the frequency and severity of outbreaks for some people.

According to an editorial published in conjunction with the study, written by Dr. David Kimberlin, an increase in genital infections could also cause an increase in infections passed from mother to child during birth. Herpes infection in newborns can cause serious diseases and even death. To prevent such transmission, mothers are tested for herpes during pregnancy. Some may be given antiviral medication toward the end of pregnancy to prevent an outbreak. Mothers with active herpes outbreaks usually have a cesarean section to prevent the baby from coming into contact with sores during delivery.

The researchers say their results point to a need for increased monitoring “to better understand the changing epidemiology of the disease, and inform vaccine development.” Other experts add that the results highlight the importance of prevention.

William Smith, executive director of the National Coalition of STD Directors, told Rewire, “What we need to remember is that the best way to prevent herpes is to use condoms when you engage in any sexual activity. This includes the use of dental dams and condoms for oral sex,” Smith said. “Whether a teen has antibodies or not, prevention remains most important not only for herpes but all other STDs as well.”

Lynn Barclay, president of the American Sexual Health Association, also spoke to Rewire about the importance of prevention efforts, especially among teens. “Young people have a good general sense of how to protect themselves against STIs but don’t always think that sex includes oral and anal sex,” Barclay said. “This is obviously misguided, given the prevalence of HSV-1 in new genital herpes infections, most of which are acquired through oral sex. We need to do a better job of encouraging a safe sex frame of mind with any sex act, and this includes educating youth about using dental dams and condoms for oral sex.”

For those who might be skeptical of adding latex to oral sex, she noted that both products come in flavored varieties.