Mike Kemp/Getty ImagesThe ad for the Beauty Pie mask appeared on the London Underground in DecemberAn advert for Beauty Pie's LED face mask has been banned for making misleading anti-wrinkle claims.
It stated the mask was "clinically proven to reduce wrinkles in four weeks" but the advertising watchdog said it did not provide enough evidence to support this claim.
Beauty Pie said it was tested by 28 people aged 30 to 65 over four weeks but the Advertising Standards Authority said this was a "relatively small" sample size.
LED technology is commonly used in medical settings to treat eczema, acne, psoriasis and sun damage, but at-home LED devices are becoming more popular.
The LED market is set to be worth £600m globally by 2032, according to analysis firm Skyquest.
However, dermatologists have told the BBC there have not been clinical trials with large enough sample sizes for long enough periods of time to know the benefits of at-home LED masks.
Beauty Pie is a direct-to-consumer, membership-based cosmetics firm which markets its products as luxury formulas with affordable prices.
Its C-Wave Light Facial LED mask costs £199 to Beauty Pie members or £299 to non-members, which the brand says is considerably cheaper than similar rival products.
The watchdog said the advert seen on the London Underground stated the mask was "skin tech that's light years ahead" and it expected "robust, product-specific evidence" to support this.
'Significant limitation'
In its response to the complaint, Beauty Pie said the results of its trial demonstrated "a significant reduction in wrinkles".
After four weeks, 92% of testers either agreed or strongly agreed with the statement that their "fine lines appear less visible", it said.
But the ASA said the way the testing was conducted "was a significant limitation" as there was no placebo group, and the sample size was "relatively small".
It also noted in its ruling that testers were asked to use an exfoliating product and a hydrogel, neither of which are sold with the mask.
The product listing on Beauty Pie's website says the mask should be used "on a clean, dry face".
"We therefore considered the reported improvements in the appearance of wrinkles could not be attributed to the [mask] alone," the ASA ruling said.
Beauty Pie said sample sizes of 20 to 25 are routinely accepted by other regulators.
The ASA said other studies that the company pointed to as evidence were "insufficient to substantiate the claim that [the mask] was clinically proven to reduce wrinkles in four weeks".
It concluded that the ad was misleading and ordered Beauty Pie not to make such a claim unless they could back it up with evidence.
BBC News has contacted Beauty Pie for comment.
