An advert for a £49 face serum has been banned over misleading claims that it made users look up to five years younger.
The billboard poster claimed the Eucerin Hyaluron-Filler Epigenetic Serum was "clinically proven" following a study of 160 people who used the product for four weeks before being asked how much younger they thought they looked.
The advertising watchdog said it had concerns over the study's methodology and the self-reporting meant the results were subjective.
Beiersdorf told the investigation it presented the claim as "up to" five years younger to reflect a genuine maximum rather than a typical result. It told the BBC its products were "supported by scientific research".
The billboard poster attracted one complaint to the Advertising Standards Authority (ASA) in November 2025 after it appeared at London's Balham Tube station.
The ASA report said: "We had concerns about the study's methodology, including that there was no control group, nor was there information about how participants were recruited."
The ASA also said that the serum was tested in a different climate to the UK, and may not work similarly.
It added that three other pieces of evidence Beiersdorf put forward to support its claim were all unpublished research, and said it had concerns about each one.
The final piece of evidence Beiersdorf submitted, a peer-reviewed study in to the active ingredient, did not include the serum.
The advert was deemed misleading and cannot appear in the same form again.
Beiersdorf said the billboard was no longer live in the UK.
It added: "All of the studies we cite are carried out in line with industry standards."
The cosmetics advertising industry can be a culprit for misleading claims, says aesthetics marketing expert Lianne Sykes, who advises firms on ethical advertising.
She said firms should do proper skin analysis over a period of time to substantiate any claims made by volunteer groups or in advertising.
She said consumers should ask questions before believing "nice branding and big names".
"How are they assessing skin quality? Is it tested on all age groups? How was success measured?," Sykes says, adding that all consumers have different skin biology and often, good skin comes from following a cluster of good habits rather than relying on a single product.
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