Image analysis of dermal collagen changes during skin aging

OBJECTIVE: To determine progressive quantitative, directional and textural changes in dermal collagen as a function of age and sex and to estimate their evolutive trend with appropriate regression models. STUDY DESIGN: Ninety-six samples of abdominal skin from autopsy cases were analyzed. The ages ranged from 3.5 months to 86 years. Picro-Sirius-stained slides were examined by polarizing microscopy, and spatial density, directional features and texture of collagen were measured by computerized image analysis. Nonlinear regression models were built to estimate evolutive changes with respect to age. The relationship between spatial orientation of collagen bundles and age was best modeled by linear regression. RESULTS: The evolutive patterns of dermal thickness and spatial density of collagen bundles correspond to a second-order polynomial model with a progressive increase from childhood to middle age and a relatively sharp decrease after the seventh decade. The evolution of textural pattern of dermal collagen, defined by gradient analysis, depicts a sort of inverted U. Its complexity is maximum in the first year of life, decreases until the period 25-50 years and increases progressively after the sixth decade. The horizontal orientation of collagen bundles with intermingled fascicles oriented in other directions, shown by young individuals, is progressively simplified with aging. In elderly subjects, collagen bundles have a horizontal orientation. No significant sex-related differences were found. CONCLUSION: Dermal collagen changes related to aging are apparently independent of sex, at least in abdominal skin, and show characteristic curvilinear evolutive trends defined by decreased dermal thickness in the elderly, decrease in the spatial density of collagen bundles and increase in textural heterogeneity of the dermis. Progressive simplification in the orientation of collagen bundles leading to a predominant horizontal disposition followed a linear trend. These changes could contribute to providing a substantial morphologic basis to age- associated biomechanical alterations in the skin.