As the rough adjacent hairs rub against each other, transfer of electrons can produce a static electrical charge. The result is the dreaded affliction of fly-away hair. Ideally, a shampoo should smooth down the cuticle and cover it with a clean coating of a sebum-like material. The smoothing effect is readily achieved by controlling the shampoo's acidity. Humectants, which help to retain moisture, also are added.
Examples are glycerol or propylene glycol, which is related to active ingredients in antifreeze.
These form strong bonds to water and prevent it from evaporating. Replacing soiled sebum with a clean protective coating is a more formidable task. Silicones such as dimethicone are relatively non-greasy materials resembling sebum. They can coat the hair, add gloss and provide a smooth surface to ease combing. They also can fill in damaged areas where the cuticle has been worn away and change hair's reflective properties, producing more shine.