McBride's clinical review on heterosexual anal intercourse and other forms of anal sexual activity, it is suggested that changing norms may affect the frequency of heterosexual anal sex. For example, besides the risk of HIV transmission being higher for anal intercourse than for vaginal intercourse,    the risk of injury to the woman during anal intercourse is 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. A study found that The Larco Museum houses an erotic gallery in which this pottery is showcased. Women engaged in anal intercourse less commonly than men. Because of this, men who have sex with men have a high risk of this cancer. When asked what techniques they used in their last ten sexual encounters, lesbians in their 30s were twice as likely as other age groups to engage in anal stimulation with a finger or dildo. In some people, ASA may cause autoimmune infertility. The review suggests that anal sex is exotic among the sexual practices of some heterosexuals and that "for a certain number of heterosexuals, anal intercourse is pleasurable, exciting, and perhaps considered more intimate than vaginal sex". In pornography, anal sex is commonly portrayed as a desirable, painless routine that does not require personal lubricant ; this can result in couples performing anal sex without care, and men and women believing that it is unusual for women, as receptive partners, to find discomfort or pain instead of pleasure from the activity. In , a non-scientific study Munson was conducted of more than members of a lesbian social organization in Colorado. This may be because of the taboo nature of anal sex and that teenagers and caregivers subsequently avoid talking to one another about the topic. Anecdotally, it is a substantial number. Greek artwork of sexual interaction between men and boys usually depicted fondling or intercrural sex , which was not condemned for violating or feminizing boys,  while male-male anal intercourse was usually depicted between males of the same age-group. This is sometimes termed technical virginity.