Nudity
Bathing is known for its benefits to health and well-being. Many societies also bathe for purification before or after other activities. Nude bathing in natural hot springs, steam rooms, and sweat lodges have existed since the Stone Age, and are found worldwide. Public bathing is not always "open to the general public". There are fees, and rules that are understood before entry. Often there is separation by gender, but not always. In Japan, Finland and Germany, mixed gender bathing or using a sauna nude is a social activity. The Japanese idea of hadaka no tsukiai, or spending time together naked, means classmates, teammates, fellow employees, families or neighbors spend time together naked for social bonding. Usually, this is while bathing at a bathhouse or onsen. As the 21st century proceeds, fewer bathhouses in Japan are mixed gender. South Korean bathhouses (Jjimjilbang) have always been gender-segregated, but nudity is required. Although there may be local differences, in the United States, it is generally understood that nudity is not allowed in public saunas. This includes being wrapped only in a towel. Instead, the rules are only about what to wear, bathing suits or loose clothing. This is true even though most US saunas are in the single-sex areas.