Teens have as much unsafe sex with their main sex partners as they do with their casual sex contacts, Brown University researchers report.

Sexually active teens say they use condoms more often with casual sex partners than they do with their main sex partners -- that is, someone they consider a spouse, a lover, a boyfriend, or a girlfriend.

But whether it's with main or casual sex partners, teens report some 20 unprotected sex acts per three months. The finding comes from a study of 1,316 sexually active teens. Celia M. Lescano, PhD, of Bradley/Hasbro Children's Research Center and Brown University was one of the researchers.

"Unfortunately, this reveals that teens may overestimate the safety of using condoms most of the time with a casual partner and underestimate the risk of unprotected sex with a serious partner," Lescano, said in a news release. "Given these high rates of unprotected sex, teens in both groups may be at risk for contracting HIV and sexually transmitted diseases."

Lescano and colleagues report their findings in the September issue of the Journal of Adolescent Health.

Different Sex Partners, Different Risks

Lescano and colleagues recruited teens in three U.S. cities: Atlanta, Miami, and Providence, R.I. The teens ranged in age from 15 to 21 with an average age of 18. Recruited from primary care clinics and outreach efforts, 49% of the teens were black, 24% were Hispanic, and 20% were non-Hispanic whites. More than half (57%) were female. All were heterosexual.

The teens completed audio, computer-assisted self-interviews. They were asked about their sexual activity over the past 90 days. For each sex act, they were asked whether their partner was a "spouse, lover, or boyfriend or girlfriend." If so, the partner was considered a main partner; if not, a casual partner.

More than a third of the teens -- most of them males -- reported sex with a casual partner. Those with casual partners averaged more sex partners (3.24) than those reporting main partners (1.34). About 10% of teens with main partners also reported casual partners.

As previous studies have shown, teens used condoms more often during vaginal and anal sex with casual partners than with main partners. Even so, they used condoms only half the time -- far too little for protection from sexually transmitted diseases. And teens with main partners used condoms only 37% of the time.

As might be expected from these findings, teens with main partners reported having had as many sexually transmitted diseases as those with casual partners.

Serial Monogamy Not Safe Sex Strategy

Why do teens have so much unprotected sex? It's not at all clear. Obviously, teens consider casual sex partners risky. Yet Lescano and colleagues find that teens' decisions to use condoms are based more on a partner's attitudes toward condoms than on their own perception of risk.

And teens may feel a false sense of security about main partners. It's false security because so many teens with main partners also have casual partners. And it's false because serial monogamy -- having one "main" partner for a brief time and then another -- isn't an effective safe-sex strategy.

"Sexual health may be jeopardized when one partner views the relationship as a mutually committed one and the other partner does not," Lescano and colleagues note. "Given the high frequency of multiple partners, partner type ... does not confer safety."

The researchers conclude that when advising teens on safe sex, it's important to stress the need for consistent condom use -- regardless of the teen's feelings toward the partner, sense of the partner's commitment, or the length of the relationship.