The ‘Factory Girl’ actress – who is expecting her first child with fiance Tom Sturridge – had a disastrous experience when she applied a Henna-based colour to her tresses, leading her to take drastic action to help get rid of the “green tinge” some time later.
She said: “I’ve had some real hair disasters. I once used henna to dye my hair brown for an audition, thinking I was being clever because it’s all natural. “Little did I know it was the worst thing I could’ve done as it coats the follicles so nothing else can penetrate and I ended up having to put ketchup on it for about a year to get rid of the green tinge.”
Sienna spends a lot of time looking after her hair because it frequently feels brittle and dry, but she insists it isn’t essential to spend a lot of money to get it back in good condition.
She told Marie Claire magazine: “Because I have to mess with my hair so much for work it gets pretty dry and I’m constantly looking for products to put back the moisture.
“Recently I’ve discovered Philip Kingsley’s Elasticizer Pre-Shampoo Treatment, which I love.
“But I don’t think you have to spend a fortune – the Aussie 3 Minute Miracle stuff is great.”