Homosexuality and heterosexuality seem to be artificial terms defined by human society obsessed by order. Human traits can be genetically determined in two ways: discrete, like eye color, or along a continuum, like height. Studies have shown that sexual orientation actually lies on a smooth continuum and the way people state their orientation is often a poor predictor of their true sexual behaviors.

Less than 10 % of people seem to be "pure" heterosexual or homosexual and on average, females are more inclined than men towards a homosexual orientation. In the end, sexual orientation range and flexibility or "choice" of the person in expressing that orientation, do matter. And higher acceptance towards bisexual men could lower their secrecy and potential health risks.

"Bisexual men have long been the object of scorn from both heterosexual and homosexual individuals and communities. Until we begin to accept that individuals are not 'black-and-white' in terms of their sexual orientations and behaviors, the myths and stereotypes surrounding male bisexuality will continue to flourish," said Brian Dodge, associate director of the Center for Sexual Health Promotion at Indiana University Bloomington, whose collaborators at Columbia University and the University of Florida have investigated in the last five years New York City black and Latino bisexual men.

The team shows that HIV prevention efforts must target both women and men regarding their male partners, as they can be bisexual. Especially black bisexual men are more prone to HIV transmission compared to other categories.

"Evidence of bisexual men's female and gay male partners expressing intolerance toward bisexuality clearly warrants broader social and structural interventions with women and gay men, with the aim of increasing awareness and acceptance of bisexuality, if disclosure is to become an expectation among bisexual men," said Dodge.

"These men do not appear to live in a vacuum in terms of knowledge and awareness of the potential risks associated with their sexual behaviors. Rather, they exist within a society which is, on the whole, extremely ignorant and intolerant of their bisexual attractions, desires, and behaviors - so secrecy and risk should really come as no surprise," he added.

The research team encountered risks specific for bisexual men. 60 % of the black bisexual men used a condom while having sex with a female partner even if she used contraceptive methods, especially for preventing undesired pregnancies. But about 50 % of the bisexual subjects did not use condoms with specific female partners, as they regarded them as less likely to be HIV infected.

Bisexual men found it easier to disclose their bisexuality with male sexual partners than to female sexual partners, especially if the other man was bisexual, too. They stated that male bisexuality appeared "bothersome" to women and gay men, and disclosure could come with severe physical, emotional and social risks (from violence to public humiliation and even crime). That's why even if most bisexual men wanted to speak openly with their wives and girlfriends, they were forced not to do it.

"Many of our participants lived in areas in which they could be seriously harmed if their bisexuality was publicly known. In reality, these men have very logical reasons for why they do not typically disclose their bisexuality," said Dodge.

"As long as the Centers for Disease Control and Prevention and other public health entities continue to polarize HIV transmission in the mutually exclusive categories of 'men who have sex with men' (MSM) and 'heterosexual,' without specifically looking at the intersection of these groups, we will continue to live in the dark in terms of understanding the sexual behavior and potential risks of bisexual men," he added.