A new study found that heterosexual and homosexual men and women don't believe bisexuality is a real orientation, CBS News reported.

Researchers from the University of Pittsburgh found that 15 percent of the adult population they surveyed had serious doubts about bisexuality being a "legitimate sexual orientation," an attitude that can encourage negative health outcomes in people who identify as bisexual.

"Bisexual men and women face prejudice, stigma and discrimination from both heterosexual and homosexual people," Dr. Mackey Friedman, researcher and director of Project Silk, an HIV prevention initiative, said in a statement.

Researchers, based on the study, found the overall opinion towards bisexuality was a negative one.

"This can cause feelings of isolation and marginalization, which prior research has shown leads to higher substance use, depression and risky sexual behavior," Friedman said. "It also can result in lower rates of HIV testing and treatment."

According to researchers, respondents were generally negative in terms of their attitudes toward bisexual men and women. Based on the study, white men who identify themselves as heterosexual are three times more likely to categorize bisexuality as "not a legitimate sexual orientation."

Women, white people and people who identified themselves as lesbian, gay had less bias and prejudice against bisexual people than white heterosexual men.

Participants who identified as gay or lesbian responded significantly less positively toward bisexuality than those who identified as bisexuals, which indicates that even within lesbian gay bisexual transgendered questioning community, bisexuals face profound stigma.

Friedman said the study highlights reasons why a bisexual person might feel the need to be secretive about their sexual orientation, something that, according to the study, could lead to higher depression and many other negative health outcomes.

"[This study] is very useful to people trying to fight stigma and marginalization," he said in a statement. "This information can guide social marketing interventions and outreach to reduce that stigma, and improve rates of HIV prevention, testing and treatment within the bisexual community."

In addition, these findings indicate that male bisexuals likely suffer more stigma than female bisexuals

Building on previous work reviewing attitudes toward bisexual men and women, researchers surveyed hundreds of adult college students for words that come to mind when they think of bisexual people, such as "confused," and "experimental," according to a press release. Then researchers developed a 33-question survey and administered it to an online sample of 1,500 adults.