Non-invasive in vivo techniques to differentiate photodamage and ageing in human skin

It is important to differentiate skin changes due to the intrinsic ageing process from those due to chronic photodamage in the development of therapies to assist the latter condition, and in this study we have used instrumental techniques to differentiate between changes in a range of properties of skin due to ageing and those due to photodamage, especially with regard to elasticity. We measured three sites of differing sun exposure in a group of younger and in a group of older subjects. A pulsed A-scan ultrasound system was used to measure skin thickness, and a uniaxial extensometer was employed to assess elastic properties. Skin surface roughness measurements were made using silicone rubber impressions and a stylus profilometer. We demonstrated significant differences in skin roughness between young and old subjects at every site and differences between sun-exposed and sun-protected sites only in the older group. Parameters of the elastic properties of skin differed between the groups, and also between sites of most different sun exposure. The uniaxial extensometer can demonstrate a loss of the skin's elasticity predominantly by photodamage, and the roughness of the skin surface can be shown to increase mostly by chronological ageing but to decrease modestly by photodamage. This demonstrates that differences between the two processes can be quantified, and indeed they should be.