Contrary to what you might think, excessively washing your hair isn’t a good option and it will actually make it become greasy faster. Hair becomes oily because the scalp produces too much sebum, not because it's dirty, and washing hair too often leads to increased sebum production. In order to break this vicious circle, you should try washing your hair less – once or twice a week maximum to regulate excess sebum. Between washes consider using a dry shampoo!