Two polar bears have turned green at Singapore Zoo as a result of algae growing in their hair.

The usually white coats of Sheba and her 13-year-old son Inuka, Singapore Zoo's two polar bears, have changed colour due to the growths in their hollow hair shafts, said Vincent Tan, a spokesman for the zoo.

"The harmless algae is the result of Singapore's warm and humid tropical conditions," Mr Tan said.

Polar bears have clear hair shafts which appear white because they reflect light.

Sheba's coat was successfully bleached with hydrogen peroxide two weeks ago and Inuka will be given a similar treatment in three weeks time, Mr Tan said.

Inuka remains mottled with bright grass-coloured splotches behind his ears, on his back and legs.