Human skin provides protection from the environment and facilitates flexibility by the reversible
deformation of its structure. In this study, we used cutometry to characterise the consequences of chronological
(intrinsic) skin ageing and chronic sun exposure on the biomechanical properties of skin from young (n=21; 18-30
years) and old (n=18; >65 years) black African-American subjects. We then related these findings to underlying skin
histological architecture.
We found that skin from buttock and forearm of young African-American subjects has similar biomechanical
properties: resilience (capable of returning to its original position following deformation); exhibits minimal fatigue; and
is highly elastic. Histologically, skin from young individuals exhibits strong interdigitation of rete ridges and an
abundance of candelabra-like arrays of elastic fibres (immuno-positive for fibrillin-rich microfibrils [FRM] and elastin).
Intrinsically aged skin is significantly less resilient (P<0.01) and less elastic (P<0.001) than young skin and is
characterised by modest effacement of rete ridges (P<0.05) and reduced deposition of FRM (P<0.001). In chronically
sun-exposed forearm, significant impairment of all biomechanical properties (P<0.001) with flattening of rete ridges
(P<0.001) and depletion of elastic fibres (both FRM (P<0.001) and elastin (P<0.001)) was apparent.
This study identifies that disruption to the highly organised elastic fibre network and effacement of rete ridge structure
in aged black African-American forearm and buttock coincides with a marked decline in biomechanical function. We
conclude that in skin of colour, despite the photoprotective properties of melanin, chronic sun-exposure exacerbates
skin ageing at both the histological and functional level.

The impact of ageing and chronic sun exposure on the biomechanical function and histological composition of black African-American skin