risk of injury to the woman during anal intercourse is also significantly higher than the risk of injury to her during vaginal intercourse because of the durability of the vaginal tissues compared to the anal tissues. Additionally, if a man moves from anal intercourse immediately to vaginal intercourse without a condom or without changing it, infections can arise in the vagina (or urinary tract) due to bacteria present within the anus; these infections can also result from switching between vaginal sex and anal sex by the use of fingers or sex toys. Pain during receptive anal sex among gay men (or men who have sex with men) is formally known as anodyspareunia. In one study, 61% of gay or bisexual men said they experienced painful receptive anal sex and that it was the most frequent sexual difficulty they had experienced. By contrast, 24% of gay or bisexual men stated that they always experienced some degree of pain during anal sex, and about 12% of gay men find it too painful to pursue receptive anal sex; it was concluded that the perception of anal sex as painful is as likely to be psychologically or emotionally based as it is to be physically based. Factors predictive of pain during anal sex include inadequate lubrication, feeling tense or anxious, lack of stimulation, as well as lack of social ease with being gay and being closeted. Research has found that psychological factors can in fact be the primary contributors to the experience of pain during anal intercourse and that adequate communication between sexual partners can prevent it, countering the notion that pain is always inevitable during anal sex. Unprotected anal sex is a risk factor for formation of antisperm antibodies (ASA) in the recipient. In some people, ASA may cause autoimmune infertility. Antisperm antibodies impair fertilization, negatively affect the implantation process and impair growth and development of the embryo. Physical damage: hemorrhoids and rectal prolapse Anal sex can exacerbate hemorrhoids and therefore result in bleeding; in other cases, the formation of a hemorrhoid is attributed to anal sex. If bleeding occurs as a result of anal sex, it may also be because of a tear in the anal or rectal tissues (an anal fissure) or perforation (a hole) in the colon, the latter of which being a serious medical issue that should be remedied by immediate medical attention. Because of the rectum's lack of