HRISTO P. DOBREV
*Corresponding author
Department of Dermatology and Venereology,
Medical University,
15A V. Aprilov St., 4002 – Plovdiv, Bulgaria

Abstract

By using suction device (Cutometer) we studied skin mechanical properties in a total of 52 healthy women. We found that the single application on volar forearm of emulsion containing urea increased mostly the viscoelastic parameters, while the emulsion containing complex of alpha-hydroxy acids (AHAs) increased the elastic parameters and decreased the viscoelastic parameters of the skin. The multiple applications on the face of cream containing plant extracts increased elastic and viscoelastic parameters, while the cream containing pentapeptides increased elastic and decreased viscoelastic parameters of the skin. We consider that after single application of moisturizing emulsions an improvement of the plasticity of epidermis (mainly its corneal layer) occurs that is due to increased hydration (urea) or decreased intercorneal cohesion (AHAs). The long-term application of anti-aging cream containing plant extracts improves the plasticity of the skin by increase its water content while the cream containing pentapeptides increases skin firmness by inducing the accumulation of newly synthesized collagen.

INTRODUCTION

The human skin is a complex multi-layered organ that possesses three major mechanical properties: plasticity (distension), elasticity and viscoelasticity. Skin plasticity reflects the skin's resistance to deformation (ability to undergo distension) under the influence of stress. Skin elasticity is related to skin ability to recover the initial shape after deformation. Skin viscoelasticity consists of time-dependent deformation with a "creep" phenomenon and nonlinear stress-strain properties with "hysteresis". The "creep" phenomenon is defined as a slowly elongation of the skin with a constant load over time. The "hysteresis" is related to the delayed return of the skin to its initial shape after removing the stress force. The skin mechanical properties are mainly controlled by the properties of the stratum corneum of the epidermis and by the collagen and elastin fibers, and surrounding intercellular ground substance of the deeper skin layers (1, 2).

Mechanical properties of the skin are very important for its protective function and cosmetic appearance. They change during life due to chronological and photo aging, and various externa ...