At £200 a time, just for the fish eggs, looking good does not come cheap. But she credits the gourmet delights for giving her long brown tresses an unbeatable shine.
"Catherine discovered the caviar treatment last summer and was astounded by the difference it made to her hair," said a source.
"She has an incredibly rich and vibrant natural hair colour but the creamy, almost oily nature of caviar really brings this out, making the colour even richer and making it so much more glossy. The eggs are packed with omega-3 fatty acids necessary for the formation of structural proteins. It is these proteins that repair dry and damaged hair and smooth over any split ends."
The two-hour pampering treatment at the celebrity salon, Hari's, also includes a complimentary glass of champagne and caviar canapes to nibble on.
Miss Zeta-Jones's hair is washed with a truffle-based shampoo, then smeared with the caviar, which is combed through and left to set. The sturgeon roe are liquidised prior to use, which is said to remove any odour.
Unlike many fad treatments, caviar is actually proven to work as a conditioning therapy. The essential fatty acids it contains produce collagen and keratin, two proteins vital for the appearance of sleek hair.
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