The ad for the lipstick, which has been promoted on television and in print by the model and actress Milla Jovovich, said that Invincible Platinum colour-fast, extra-comfort lipstick lasts up to eight hours "without feathering or dryness, thanks to its Colour Guard technology".
It went on to state: "Lipcolour stays flawless for hours without smudging, feathering or fading."
However a complainant from Berkshire challenged the claims that it lasted up to eight hours or stayed flawless without feathering or fading.
L'Oreal defended the claims by providing the results of an independent study of 25 volunteers as well as the results of two consumer tests, one of which compared its lipstick with competitors' products.
But the Advertising Standards Authority sought expert advice. It found that the ad claim implied that the lip colour would stay perfect on all lips for up to eight hours but because the evidence showed that some subjects experienced feathering or fading after six hours, L'Oreal had not justified the claim.
It has told the company to ensure future ads did not imply the lip colour would stay flawless for up to eight hours.
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