There are many reasons that hair can get greasy. The most obvious reason is build-up. Build-up on the hair can be caused by products, sweat, natural oil from the scalp, and even pollution. This residue on the strands can look unsightly and must be removed in order for the hair to become weightless, full, and shiny once again. Other reasons for greasy hair include genetics, environment, and your diet.  To reduce the amount of build up on your strands, try to wash your hair more frequently and using products that are more lightweight. Of course, you can also use baby powder or a dry shampoo between washes to help remove build up until your next wash.