Men who have sex with men

First, it was pursued by epidemiologists seeking behavioral categories that would offer better analytical concepts for the study of disease-risk than identity-based categories (such as "gay", "bisexual", or "straight"), because a man who self-identifies as straight may nonetheless be sexually active with other men; similarly, a man who self-identifies as gay or bisexual is not necessarily sexually active with other men.

Men who are non-heterosexual or questioning may identify with all, none, a combination of these, or one of the newer terms indicating a similar sexual, romantic, and cultural identity like bi-curious.

[6] There were no similar traits in all of the MSM population studied, other than them being males and engaging in sex with other men.

In some countries, homosexual relationships may be illegal or taboo, making MSM difficult to reach.

[7][8] The term's precise use and definition has varied with regard to transgender and intersex people, who do not fall neatly into binary sex categories.

[10] In the U.S., among men aged 15 to 44, an estimated 6% have engaged in oral or anal sex with another man at some point in their lives, and about 2.9% have had at least one male sexual partner in the previous 12 months.

[30] According to a CDC study, HIV prevalence in the MSM population of the U.S. varies widely by ethnicity.

[38] Studies have found that less than 5% of MSM in Africa, Asia, and Latin America have access to HIV-related health care.

[38] Pre-exposure prophylaxis (PrEP) is the use of medication to prevent HIV transmission in people who have not yet been exposed to the virus.

When used as directed, PrEP has been shown to be highly effective, reducing the risk of contracting HIV up to 99%.

[39] As of 2018[update], numerous countries have approved the use of PrEP for HIV/AIDS prevention, including the United States, South Korea,[40] France, Norway,[41] Australia,[42] Israel,[43] Canada,[43] Kenya, South Africa, Peru, Thailand, the European Union[44][45] and Taiwan.

[46] New Zealand was one of the first countries in the world to publicly fund PrEP for the prevention of HIV in March 2018.

[51][52] Genital human papillomavirus (HPV) is a common virus that most sexually active people in the U.S. will have at some time in their lives.

[53][55][56] Though not commonly classified as an STI, giardiasis can be transmitted between gay men,[57] and it can be responsible for severe weight loss and death for individuals who have compromised immune systems, especially HIV.

[61] Most national standards require direct questioning regarding a donor's sexual history, but the length of deferral varies.