Homemade sunscreens featured on the photo-sharing site Pinterest might look good, but most of them aren’t protective for sunburn or skin cancer, US research shows.

Lead author Dr Julie Merten, from the University of North Florida, says 95% of the posts on the site positively portrayed the effectiveness of homemade sunscreens, however, about 65% of the posts recommend recipes that offer insufficient ultraviolet radiation protection.

“This is concerning because the ingredients recommended in homemade sunscreen [posts] offer minimal scientifically proven broad-spectrum protection from UV radiation yet are widely shared and promoted as safe alternatives to commercial sunscreens on Pinterest,” she says.

Many people search for alternatives to approved, commercially available sunscreens because of concerns ranging from coral reef damage to hormone disruption, Dr Merten and her team note in the journal Health Communication.