Making promises to parents, self or even God doesn't guarantee that unmarried teenagers won't have sex. But pledging to remain celibate until marriage, at the expense of comprehensive sex education, does make them less knowledgable and less prepared when they do have sex.

A new analysis of a federal survey of 11,000 students in seventh through 12th grade in 1995, 1996 and 2001 shows that more than half of teens were sexually active before marriage, and the data was the same for those students who had taken a "virginity pledge" to abstain from sex. But -- and this is the worst part -- those youths who had taken the pledge were less likely to have used condoms or contraceptives to prevent sexually transmitted diseases and pregnancy.

Abstinence is the ideal way to prevent STDs and premarital pregnancies, but research shows that young people who rely solely on self-restraint and their parents who fail to instruct them about sex are courting disaster in the forms of disease and unwanted pregnancy.

Utah, a state where Church of Jesus Christ of Latter-day Saints doctrine and conservative beliefs about abstinence-only education prevail, is an example of the failure of "just say no" as a way to protect teens.

The HIV infection rate was up 32 percent in Salt Lake County in 2007 over the previous year, and people age 15-24 are most at risk. The rate of STD infections in Utah is increasing at nearly four times the national average, and the state health department reported this year that gonorrhea cases increased more than 280 percent and chlamydia cases more than 60 percent since 2001 statewide. Utah mirrors national teen pregnancy rates, which were decreasing earlier in this decade, but increased in 2006.

Utah's public schools provide little information about sex and its consequences. Lawmakers require schools to emphasize abstinence, and students' questions about condom use often must go unanswered.

Legislators and their conservative constituents who believe comprehensive sex education belongs at home should take note of the buildup of evidence that debunks the hollow hope that teens, with their raging hormones and immature emotional controls, can always "just say no" and mean it.

It's better for the health of our precious teens if parents and schools not only teach them the ideal of abstinence but arm them with knowledge that can help teens protect themselves if and when they decide to answer "yes."