In ancient times, washing hair was called “Mu 沐” and bathing was called “Yu 浴”.
It was very troublesome for the ancients to wash their hair, especially in the Tang dynasty, people basically didn’t wash their hair.
But they can’t stand it if they don’t wash it for a long time.
So how did they solve the problem when their hair was full of oil?
Those who have the conditions will use rice water.
Those who do not have the condition can only use plant ash.