A number of hand sanitisers sold on online marketplaces contain less alcohol that advertised, a investigation by Which? has found.
The worst-offending product was identified as Klenzy Hand Sanitizing Gel, available for sale on eBay, which claimed to have a 75% alcohol content but actually contained just 10%, according to tests by the consumer group.
Hand sanitisers need an alcohol content of between 60% and 90% to be deemed effective against Covid-19.
Sanitisers normally use ethanol, isopropanol or a mixture of the two.
Which? scientists tested 18 products available at high street retailers, supermarkets and online marketplaces.
Three purchased from the online marketplaces eBay and Etsy failed to show the same alcohol levels claimed on the product listing page or the packaging.
The VaidaMakeup Hand Sanitiser Gel, sold on Etsy, was found to have 33% instead of the 70% mentioned, while the Hansan Antibacterial Hand Sanitiser, sold on eBay, came out as 35% instead of 70%.
EBay removed both product listings and banned the sellers from selling hand sanitiser on the site again.
The seller on Etsy, meanwhile, said they had removed the listing and contacted all customers to warn them.
"We don't have final control over sellers' items but do ask they act with integrity, as was the case here, by them taking action once the issue was brought to their attention," Etsy said in a statement.
Seven products from Amazon Marketplace were also among the investigation but passed with the correct stated and required levels of alcohol content.
All other hand sanitisers purchased from high street retailers and supermarkets also matched their stated claims.
"It's extremely concerning that hand sanitisers readily available on online marketplaces eBay and Etsy make misleading claims about alcohol content and could leave consumers unwittingly exposed to the Covid-19 virus," said Natalie Hitchins, Which? head of home products and services.
Which? said it approached the sellers of the Hansan and Klenzy products for comment but did not receive a response.
It was unable to find contact details for any manufacturers.
A spokesman for eBay said: "The two listings flagged by Which? have been removed, and we've taken the appropriate action on the sellers, who will no longer be permitted to sell hand sanitiser on eBay."