Today's teens have a higher risk of contracting genital herpes than before, a new study reveals.

Research published in the "Journal of Infectious Diseases" suggests the increase in risk may be the result of fewer teens being exposed to the cold-sore causing herpes simplex virus type 1 (HSV-1) at adolescents in previous years, causing their bodies to lack the antivirus necessary to fight off the virus.

Most people contract HSV-1 in childhood just by touching the skin of an infected adult.

Both HSV-1 and the sexually-transmitted herpes simplex virus type 1 (HSV-2) cause lifelong infections with no known cure. Both viruses can cause cold sores and genital herpes, but HSV-1 is associated with fewer recurrences of genital infection, according to Dr. David Kimberlin, chair of infection diseases at the University of Alabama.  

The new study, which tracked the prevalence of herpes among 14-to 19-year-olds in the United States, found there was a 23 percent decline in HSV-1 antibodies during the 2005-2010 period compared to those studied in the 1999-2004 period.

Kimberlin said one in 10 teens who a decade ago would have had already acquired HSV-1 antibodies are more vulnerable to get genital herpes when they become sexually active.

The study said that these findings in combination with increased oral sex behaviors among young people, make adolescents more likely than those in previous time periods to acquire HSV-1 genitally.

"Every year the proportion of patients who get infected with HSV-1 through oral sex is increasing," Dr. Marcelo Laufer, a pediatric infectious disease specialist at Miami Children's Hospital, told Health Day. "Adolescents who reach that age without being exposed to HSV-1 might, through oral sex, be more susceptible to the infection.

The study shows that HSV-1 has been seen increasingly as the cause of genital herpes in industrialized countries, revealing that up to 60 percent of genital herpes cases were due to HSV-1.