Why does hair get darker when wet?
When light hits wet hair, some is reflected off the surface of the water film to be reflected or refracted again.
Asked by: Carel Lucas, Perth, Australia
When light strikes dry hair, some of it is absorbed by the pigment in the hair and some reflects back to your eyes. Water is transparent and a thin film absorbs very little light by itself. But when light hits wet hair, some of the light reflecting off the surface of the hair strikes the inside surface of the water film at the right angle to be reflected or refracted back onto the hair again. This creates a second chance for the light to be absorbed, making the hair appear darker.
Luis trained as a zoologist, but now works as a science and technology educator. In his spare time he builds 3D-printed robots, in the hope that he will be spared when the revolution inevitably comes.