A blast of sunshine could help fight skin diseases and cancer by attracting immune cells to the skin surface, according to a new study.

Eugene Butcher at Stanford University in California, US, and colleagues discovered an interesting immune process in human skin. Immune cells in the skin, called dendritic cells, convert vitamin D3 (produced in exposed skin in response to sunlight) into its active form.

This “active” vitamin D3 then causes T-cells to make surface changes that allow them to migrate to the uppermost layer of the skin, Butcher’s team found. T-cells are the immune cells that destroy damaged and infected cells, and they also regulate other immune cells.

The findings explain how T-cells “know” to go to the skin's surface once the skin has suffered some sun-induced DNA-damage, the researchers say.

“Sunshine is good for you, as long as it’s not too much,” says team member Hekla Sigmundsdottir. She points out that the skin disorder psoriasis is sometimes treated with vitamin D3 creams – it may work by moving T-cells into the skin, she speculates.

The finding adds to a growing body of evidence that dendritic cells, which live in tissues that are exposed to the outside environment, such as the skin and nose, run “traffic control” for the immune system, interpreting local conditions and directing T-cells to where they are needed.

Journal reference: Nature Immunology (DOI: 10.1038/ni1433)