The answer(s)Twice a week.
StoryHair washing is the cosmetic act of keeping hair clean by washing it. To remove sebum from hair, some apply a surfactant, usually shampoo (sometimes soap) to their hair and lather the surfactant with water. The surfactant is rinsed out with water along with the dirt that it bonds to. There are dry shampoos; powders which remove sebum from hair by soaking it up prior to being combed out.
Youtubehttps://youtu.be/owoDWIQ6F4w
Linkhttp://www.independent.co.uk/life-style/the-truth-about-how-often-you-should-wash-your-hair-according-to-science-a7020906.html