Half-baked advice? Why are influencers targeting sunscreen?

It's summertime for much of the world, and social media is awash with influencers airing their concerns about sunscreen.

- Ian Sample

Among them is the reality TV star Sam Faiers, who believes sunscreen is "full of toxic ingredients". None of her family wore sunscreen, she confessed, adding that her children had built up "a really good tolerance" to the sun. Some of the claims appear to be fueled by a US doctor who told his followers: "Be careful what you smear on yourself and your children." Here we look at the science behind sunscreen and sun exposure.

How does sunshine damage skin?

It's all down to the high-energy ultraviolet (UV) rays. These cause premature skin aging and wrinkles by degrading collagen and elastin. Collagen gives skin its firmness and structure, while elastin makes it stretchy. UV rays can also damage the DNA in skin cells, leading to mutations that ultimately drive skin cancers. One in three cancers globally is a skin cancer, and the major driver is UV rays.

Dr Claire Knight at Cancer Research UK said: "Too much UV radiation from the sun is the main cause of melanoma, the most serious type of skin cancer. That's why it's important to develop good sun safety habits from a young age and protect your skin when the sun is strong using shade, clothing and sunscreen together."

Can you develop tolerance to the sun?

When the summer sunshine arrives, the skin responds to protect itself. The outermost layer, the epidermis, thickens and many people develop a tan, as cells in the skin called melanocytes produce more UV-absorbing melanin.

Not everyone tans, though, and acquiring a tan itself results in DNA damage.

Brian Diffey, emeritus professor of photobiology at Newcastle University, said: "Most of that damage gets repaired, but some of it doesn't; it causes mutations and those can go on developing throughout life to give rise to skin cancer. Sun exposure in childhood is a critical period for developing skin cancer, particularly melanoma, later in life."