The move follows research by the Co-op, which found that three people in four still do not realise sunshine can cause skin cancer, and one in three are unaware that sun lotions can reduce that risk.
Cost is also thought to deter people from using sun-creams, some of which sell for twice the price of champagne when measured by volume.
The Co-op, Britain's biggest retailer, will sell some leading brands at cost price throughout the summer. Typically, a 200ml bottle of Ambre Solaire's Factor 15 High Protection Milk will be reduced from the recommended retail price of pounds 9.29 to pounds 5.43, and a similar-sized bottle of factor 25 Piz Buin Lotion will come down from pounds 11.49 to pounds 5.97.
A Co-op spokesman, Ged Carter, said Britons were still failing to get the message that sunbathing was dangerous and should only be done with the protection of a good sun-cream.
The survey of 2,001 adults commissioned by the Co-op found that Britons each waste an average of one day on holiday each year because of sunburn.
"It's unfortunate that the burning ambition most Britons display on holiday costs them both pain and money in wasted holiday time," said Mr Carter.
"Worse still is ignorance about the fact that sun rays on skin cancer can cause health problems in the long term."
The move has prompted at least two rival supermarket chains, which sell the lotions at or around the recommended retail price, to warn they could consider cutting their own prices.
Tesco's corporate affairs manager Martin Venning said: "Clearly we will monitor the situation and may make a decision in the future."
He added that Tesco marketed its own brand of lotions called Sun Essentials, which were substantially cheaper than designer brands, costing pounds 4.99 for 200ml bottles.
A Boots spokesman warned: "We would obviously consider the marketplace when setting retail prices."
However, Asda stressed it would not be cutting its prices, pointing out that it already offered its own brand Sun System lotions at pounds 4.99 for a 200ml bottle.
Asda spokeswoman Charlie Hobson said: "Our customers already have a choice. They can buy Ambre Solaire or they can buy our own brand which has all the same features and is cheaper."Reuse content