One wash often isn’t enough to break down all the residue and product build-up, especially if you haven’t washed your hair for a few days,” says Abramite. What would you do to the muddy t-shirt: “You’d remove the big pieces of dirt and mud before you put it in the washing machine,” says Abramite. If your shampoo doesn’t produce a lot of lather that is the sign of doubling up the shampoo round.