Keira Knightley has revealed her hair started falling out because she was dying it for film roles.

The British actress said she now wears wigs to portray characters on the big screen after dye was causing her to lose her locks.

Keira KnightleyKeira Knightley (Greg Allen / AP/PA Images)

She told InStyle Magazine: “‘I have dyed my hair virtually every colour imaginable for different films. It got so bad that my hair literally began to fall out of my head.

“So for the past five years I’ve used wigs, which is the greatest thing that’s ever happened to my hair.”

Keira KnightleyKeira Knightley (Anthony Devlin/PA)

Keira, 31, said that having a baby last year had also boosted her hair volume – and even resulted in her growing dreadlocks.

The Pirates of the Caribbean actress and her husband, former Klaxons musician James Righton, welcomed their daughter Edie in May 2015.

Keira Knightley and James RightonKeira Knightley and James Righton (Matt Crossick/PA)

Keira told the magazine: “I have naturally crazy, curly hair, and since I’ve had the baby it’s become 10 times thicker. So now I’ve been finding quite a lot of dreadlocks.”

Keira, who was nominated for an Oscar for her role in The Imitation Game, is reportedly set to star as the Sugar Plum Fairy in a new Disney live-action version of The Nutcracker.