Skin tensile properties revisited during ageing. Where now, where next?

Skin and its subcutaneous layer represent a complex composite of tissues, whose mechanical characteristics depend upon the mutual interdependence of their constituent parts. The molecular and microanatomical structures of skin allow it to meet normal mechanical demands. They also determine the orientation both of Langer's lines and of relaxed skin tension lines. Ageing, photodamage, hormones, drugs, cosmetic products and dermatological interventions may modify the skin's overall tensile properties. In turn, any variation in mechanical stresses and strains imposed upon the skin's connective tissue influences the metabolic activity and phenotypic expression of fibroblasts and dermal dendrocytes. The viscoelastic functions of ageing skin can be tested by altering the orientation and magnitude of imposed stresses and strains over time. Assessment can be made of various biomechanical properties of skin: tensile, torsional, acoustic shear wave, indentation, impact and elevation. Such objective biomechanical assessments may be applied to dermocosmetic interventions, so providing opportunity for progress in cosmetic dermatological science.