Sunscreen does two important jobs. It is largely used for its UVB protection benefits – blocking the rays that cause sunburn and are a major contributor to the development of skin cancer. But it also blocks UVA radiation, filtering out the rays that lead to signs of ageing.

Vitamin C does neither of these things, says Rosalind Simpson, a professor of dermatology at the University of Nottingham. That said, it is thought to help prevent sun damage in a different way.

“Antioxidants such as vitamin C have become a hot topic,” Simpson says. “People are really interested in whether they can improve skin appearance by neutralising free radicals created by UV exposure and pollution. Those free radicals contribute to the breakdown of collagen and loss of skin firmness.”

Whereas sunscreen acts as a kind of UV filter, antioxidants are thought to provide an additional line of defence. UVA exposure generates unstable free radicals in the skin, which can damage cells by disrupting their structures, and Vitamin C is believed to stop them doing this.

A 1996 study examined the effectiveness of antioxidants, including vitamins C and E, with and without sunscreen, in protecting against UV-induced skin damage. It found that vitamin C appeared to enhance protection against UVA-induced skin damage, but only when used alongside sunscreen. The researchers concluded that antioxidants may provide additional protection when combined with established sun-protection products.

“Nothing is a substitute for a good quality, broad-spectrum sunscreen with UVA and UVB protection and sensible habits when in the sunshine,” says Simpson.

That means wearing sunscreen, reapplying it regularly, and limiting direct sun exposure during the hottest parts of the day.