Sunscreen is a multi-billion dollar industry. We’ve long been encouraged to apply it daily, to block out the sun’s rays. But one dermatologist argues some sunlight is necessary and sunscreen could be preventing our skin from carrying out a vital function. Dr Richard Weller explains what happened when he took his findings to sunscreen manufacturers. Also in the programme, Holly Thaggard, founder and chief executive of Supergoop, tells us why US regulators are taking a closer look at common sunscreen ingredients.