In the context of consensual erotic activities, sadism and masochism are not strictly accurate terms; there is a significant difference from the medical or psychological usage of both terms. Masturbation has been depicted in art since prehistoric times and is mentioned and discussed in very early writings. However the genre remains a very small proportion of the pornographic DVD market; for example at porn retailer HotMovies. Actors are mostly amateur; any well-known actors in bisexual porn tend to be from the gay pornography industry. Erotic spanking is the act of spanking another person for the sexual arousal or gratification of either or both parties. Squirt pornography involves women ejaculating. When all regions of the face are included, facial cum shots comprise approximately 62% of scenes where external ejaculation occurs. Twink pornography features younger performers, and usually features young men under 30 who identify as gay or bisexual. There is also some evidence that pornography can be used to treat voyeurism. Buck Angel is the best-known actor in this genre. Bukkake, Gokkun, Omorashi, and tentacle erotica are few uniquely Japanese genres known to western viewers. Bareback sex is physical hentai porn sexual activity, especially sexual penetration, without the use of a condom. The related term twinkle-toes, which implies that a man is effeminate, tends to be used in a derogatory manner. Enema pornography involves adults given enemas to others, often fake. Individuals who can change between top/dominant and bottom/submissive roles—whether from relationship to relationship or within a given relationship—are known as switches, though the term switch in this context is occasionally seen as derogatory and is rejected by many who might simplistically fit the definition. As with most forms of naked milf sexual activity, anal sex participants risk contracting sexually transmitted infections . Gonzo porn is influenced by amateur pornography, and it tends to use far fewer full-body/wide shots in favor of gay twinks more close-ups .
