A trial investigating the health benefits and risks of spending time in the sun is being launched in Manchester today.
This Cancer Research UK-funded trial will use simulated sunlight to determine whether certain amounts of sun are beneficial for certain skin types, and how much is too much.
The amount of sun exposure needed to make enough vitamin D, the 'sunshine vitamin', varies from person to person, largely dependent on skin colour.
Study leader Professor Lesley Rhodes, from the University of Manchester, said: "There's no doubt that too much sun can seriously increase skin cancer risk, but we know there are also important benefits to going out in the sun, such as making enough vitamin D.
"This study is about finding that balance, so we can offer people of all skin colours the best possible advice about how much sun is safe for them."
Seventy-five healthy volunteers aged 18 to 45, with a range of skin colours, are being recruited to take part in the study at Salford Royal Hospital.
Sara Hiom, director of information at Cancer Research UK, said: "Sun is a really important source of vitamin D, but the amount of sun needed varies from person to person.
"Studies like this, which use simulated sunlight so we can compare the results for people with different skin types, will tell us much more precisely how much sun is safe for different people.
"In the meantime, continue enjoying the sun, but remember that the amount of time you need to spend in it to make enough vitamin D is always less than would make your skin redden.
"The best way to protect your skin from sunburn is to use shade, clothing and at least factor 15 sunscreen applied generously and regularly."