As a barber, I summed up that it is best to wash my hair once every few days:

The frequency of hair cleaning varies from person to person, depending on your scalp oil secretion, daily activity level and climatic conditions.

Generally speaking, if your scalp is greasy, you can consider washing your hair every day; If your scalp is dry, you can wash it every two or three days. It depends on the needs of your scalp and hair.