The average and healthiest length of time is 4-5 days, making sure that you wash the scalp specifically, and then condition mid shaft and ends, and working through remainder conditioner on the roots. The sebaceous glands produce sebum, which is a natural moisturizer and protectant to the hair. Allowing that sebum to be brushed through the hair from roots to end creates shinier and healthier hair. Washing the hair too often, will result in “greasier” hair because you sent the sebaceous glands into over drive of producing sebum.