Since ancient times, human beings have been trying to protect their skin against the adverse effects of the sun. From the first
mineral sunscreens used by Egyptians, to the current more sophisticated ultraviolet (UVA/UVB) organic
sunscreens, progress has been made in terms of sun protection and deeper knowledge of skin physiology has been acquired in the process. The solar spectrum is composed of radiations of various wavelengths having specific, as well as overlapping effects on skin. UVB is mainly responsible for
sunburn and
DNA dimer formation that can lead to mutation. UVA generates oxidative reactions affecting
DNA,
proteins and
lipids, and is also immunosuppressive. Recently, visible light and infrared radiation (IR) have been associated with oxidative damage and IR has been additionally linked to adverse heat effects on skin. Numerous other extrinsic factors, related to environment and lifestyle, also affect the appearance of skin, precipitating ageing. New molecular mechanisms linking sun and environmental factors to skin ageing have been identified: IR affects mitochondrial integrity and specific heat receptors also mediate some of its effects,
tryptophan is a chromophore for UVB, and the
aryl hydrocarbon receptor (AhR) is activated by light and
xenobiotics to alter skin physiology. Integrating all these new
elements is changing the way we think about skin extrinsic ageing. Is UVA/UVB
sunscreen protection still enough for our skin?