Commercial baths during the Kamakura period: 1185 to 1333
Due to the small opening, the lack of windows, and the thick steam, these baths were usually very dark, and customers often cleared their throats to signal their position to others. It can safely be assumed that on occasions an amorous couple used the dark room for more than mere bathing, and also amorous singles may have less-than-accidentally bumped into members of the other sex.
Bathing in the Edo period:1603 to 1867
At the beginning of the Edo period, there were two types of baths common in different regions. In Tokyo (then called Edo), the normal bath was a regular bath with a pool called yuya (窶懌?吮?ｰﾂｮ, lit. hot water shop), whereas in Osaka a bath was a steam bath with only a shallow pool and was called mushiburo (ﾂ湘ｶ窶堋ｵ窶｢窶藩廚, lit. steam bath), or just furo (窶｢窶藩廚).
At the end of the Edo period, the Tokugawa shogunate (1603 to 1868) at different times required baths to segregate by sex to preserve public morals. However, many bath house owners simply added a small board to separate the bath, with little effect for the preservation of morals. Other baths had men and women bathe at different times or different days, and some baths limited themselves entirely to female or male clientele. The laws about mixed-sex bathing were soon relaxed again.
One reason for the popularity of the baths were the female bathing attendants yuna (窶懌?卍鞘?? lit. hot water woman). These attendants helped the customers by scrubbing their backs. However, after the bath officially closed, many of these women sold sex to male customers. Even nowadays, some brothels in Japan specialize on having young women clean their male customers in a private bath. These establishments are called sōpu rando (ﾆ箪ﾂーﾆ致ﾆ停?ｰﾆ停?愴檀, lit. soap land).
Subsequently, the Tokugawa shogunate limited the number of Yuna to three per bath house, to preserve the public morals. However, this rule was widely ignored, and shortly thereafter in 1841 the Tokugawa shogunate prohibited any Yuna to serve in a bath house, and furthermore prohibited mixed-sex bathing again. Large numbers of unemployed Yuna thereafter moved to the official red-light districts to continue their services.
Up to 1970 there were also male washing assistants called sansuke (ﾅｽOﾂ鞘?｢, lit. three helps) for washing and massaging both male and female customers. These male workers, however, usually did not participate in prostitution.
The prohibition of mixed-sex bathing again did not last long, and when Commodore Perry visited Japan in 1853 and 1854, he was displeased about the lack of morals due to mixed sex bathing. Subsequently, the Tokugawa shogunate prohibited mixed sex bathing again.