Anti-wrinkle creams promoted by leading cosmetics firms for removing wrinkles and "plumping" skin does no good, scientists have said.
They say that the collagen molecules in the enticing-sounding lotions and potions are so large that very few make it through the skin.
As a result, they sit on the surface of the face until they are rubbed off or washed away. In other words, money spent on their products is, quite literally, going down the drain.
The criticism follows a survey of experts' pet hates conducted by the charity Sense About Science.
L'Oreal's Wrinkle Decrease Collagen range is aimed at women aged 35-plus and claims to "reduce the appearance of wrinkles and creases".
The firm's Paris Dermot Expertise Collagen Micro-vibration eye cream costs around 11 pounds for a tube containing 15ml, or three teaspoons worth. It contains collagen "biospheres" said to have the power to combat crows' feet, dark circles and bags under the eyes.
But scientists have disputed the claims made by many beauty firms, saying the collagen molecules used are too large to penetrate the skin's outer surface.
"The idea created by many of these products is that collagen can get through the upper layers of skin and reinforce our own natural collagen, but this is preposterous," the Daily Mail quoted Richard Guy, professor of pharmaceutical sciences at the University of Bath, as saying.
'The simple fact is that collagen is a huge molecule and the skin is designed to keep such substances out.
Dr Blanca Sengerova, an Oxford University protein biochemist who works on the chemistry of large molecules says: "It really frustrates me when I see adverts for anti-wrinkle creams containing collagen.
"Although collagen is structurally important for the integrity of our skin, the protein molecule is far too large to pass through the barrier posed by the skin," Sengerova added.