A polar bear is not white
The hairs of a polar bear are unpigmented and translucent. The skin underneath is black. The coat looks white because the hairs scatter visible light.
Established2 min read
Each hair is a hollow, pigmentless tube. Scatter enough of them and the reflected light is broadband, which the eye calls white. Under the coat the skin is black, useful for absorbing whatever radiation reaches it. Photographs of shaved skin, and of wet bears, show it.
A popular extra claim, that the hairs are fibre-optic cables piping sunlight to the skin, does not hold up. The hairs scatter and absorb; they do not function as light guides in any important way. The colour story does not need them to.
Caveats
- In some light a bear looks yellow or grey. That is soiling, angle, and the spectrum of the sky, not a second pigment.
- Cubs are born with the same arrangement. Pink noses and dark eyes are skin showing through.
Sources
- 1Grojean R. E., Sousa J. A., Henry M. C.. Utilization of solar radiation by polar animals: an optical model for pelts. Applied Optics 19, 1980.