Men who have sex with men with regard to trans women, people born either biologically male or with ambiguous genitalia who self-identify as female. Some sources consider trans women who have sex with men to be MSM, others consider women who are trans "alongside" MSM, and others are internally inconsistent (defining transgender women to be MSM in one place but referring to "MSM and transgender" in another). Determining the number of men who have ever had sex with another man is difficult. Worldwide, at least 3% of men, and perhaps as high as 16% of men, have had sex at least once with a man. These
Men who have sex with men individuals who have compromised immune systems, especially HIV. Unprotected anal sex is a risk factor for formation of antisperm antibodies (ASA) in the recipient. In some people, ASA may cause autoimmune infertility. Many countries impose restrictions on donating blood for men who have or have had sex with men, as well as their female sexual partners—see the maps. Most national standards require direct questioning regarding a donor's sexual history, but the length of deferral varies. Men who have sex with men Men who have sex with men (MSM), also known as males who have sex with males, are male persons