The Romans used to scrape dirt and oil off their skin, bathe in hot water, and apply olive oil afterward. Soap wasnāt actually invented till after the collapse of the Empire, if I have that right.
I learned to my surprise that it is animal fat that tends to give soap its harshness. The first soap made with plant fat was Castile soap, made with olive oil, and it was prized for bathing, because of its gentleness on the skin.
In The Dirt on Clean, by Katherine Ashenburg (which is a fun read, by the way), it appears that various bathing habits are possible without ill effects, all the way from not bathing at all to the American habit of a thorough daily shower with lots of chemicals.
During the plague years, French doctors became convinced that bathing was actually harmful, and they recommended wearing linen clothing as a substitute. Louis XIV was considered exceptionally clean, because he changed his linen shirt three times a day. But as Ashenburg remarks, āat no point in history does it appear that the human race ever became too smelly to reproduce.ā A lot of our ideas on the subject of cleanliness apparently boil down to habit and custom.