What kind of soap/shampoo was used in medieval Japan (circa 1600 AD)?

http://en.wikipedia.org/wiki/Soap

Early history

Soapnut Tree (Reeta / Sapindus tree)
The earliest recorded evidence of the production of soap-like materials dates back to around 2800 BC in Ancient Babylon.[8] A formula for soap consisting of water, alkali and cassia oil was written on a Babylonian clay tablet around 2200 BC.
The Ebers papyrus (Egypt, 1550 BC) indicates that ancient Egyptians bathed regularly and combined animal and vegetable oils with alkaline salts to create a soap-like substance. Egyptian documents mention that a soap-like substance was used in the preparation of wool for weaving.

Stocky’s answer about the availability of Soapnut seems a credible one. Western-style soap made from animal fat was first produced in Japan in 1870. (source).

Still, it’s questionable whether any soapy product was commonly used for cleansing. Prior to the beginning of the modern era, bathing held an important place in Japanese society for many reasons (social, religious, recreational, ritual, etc.)(source), but cleansing was not among them. It was the custom to wash oneself before entering the bath so as not to foul the bathwater (which was typically used by many people before being thrown out) . Abrasion was the method of choice for cleaning: “bathing in Japan seems to have involved a preliminary cleansing with exfoliant material and scoops of cold water from a bucket (one of the earliest American visitors to Japan remarks that “sand does duty for soap” in Japan; see Edward Yorke McCauley, With Perry in Japan, ed. Allan B. Cole, Princeton University Press, 1942, p. 105, entry for April 21 1854). Only when clean did one enter the tub of very hot water, whose primary purpose was to relax a tired body.”
(source)

Here is a source that lists it and the price in 1750, placing it a century before 1854. Scroll down to see chart.

While the western style animal fat soap was first “produced” in japan in 1870 it was already being imported from other countries.

That would explain the high price shown on the chart at that early date (although the footnote makes the cryptic statement that the soap price shown is a guess based on the price of oil).

…and shipping costs, Harp. Which was really wild and all over the charts. Shortly after the California gold rush, while the area was being settled, it wasn’t uncommon for laundry to be shipped to Hawaii, rather than other places on the west coast because the cost was so high. That also influenced the Chinese laundry trade as well.

There are a few references in Hagakure to people bathing with ashes as soap.

Ashes (lye) and fat are the two classic soap ingredients.