Hairbrushes should be washed frequently, and the correct way to do this, so that the backs of the brushes are not damaged, is to fill a basin with cold water and add a little baking soda or ammonia. Tip the basin sufficiently to allow the brush to be swished up and down in the water without wetting the back. Rinse in clear water, shake vigourously, and stand on its side on the sill of an open window to dry. Never wash in hot water or allow to lie on the back when drying.