The skin plays the key role of physical barrier between the inside and the outside of the body and, as such, is one of the most responsive organs to external aggressions.
Among all environmental factors responsible for extrinsic ageing, repeated UV (ultraviolet) exposure is the most significant and photoageing is the major consequence. Photoaged skins feature a set of typical modifications: wrinkles and fine lines, altered microrelief and coarse skin, lack of luminosity and pigmentary disorders.
Comparing UVA & UVB’s impacts on the skin
Within the UV spectrum, UVB rays have, for a long time, been considered more genotoxic than UVA for the epidermis.
Indeed, due to its wavelength, UVB has a capacity to penetrate into the heart of keratinocytes, down to the DNA, where it generates photoproducts (such as cyclobutane pyrimidine dimers or CPD) and direct DNA lesions. On the skin, the effects of UVB rays are visible through local inflammation and sunburn.
On the contrary, UVA rays have the capacity to penetrate deeper layers of the skin.
Until recently, their effects were thought mainly limited to structural alterations of the dermis (breakdown of collagen and elastin networks among others) and oxidative stress.