Fig. 4.

Proposed evolutional model from the histopathological parameters throughout life. After birth, the skin has a high density of fine bundles of collagen, in a parallel disposition in the reticular dermis. Progressive development and remodelling of the tissue cause several observable changes during adult life: the density of the bundles is reduced in the reticular dermis, but these bundles reach their maximal thickness and disposition in the three directions of the space, which conditions an increase in the thickness of the reticular dermis; in the papillary dermis, on the other hand, the density is kept stable but the bundles lose thickness and the papillary dermis increases its width. Finally, in the last stage of life during the intrinsic cutaneous ageing the collagen bundles lose density and thickness both in the papillary and reticular dermis, and, in this last localisation, the collagen is again disposed in a parallel manner. The reticular dermis becomes thinner but the papillary dermis continues to increase in thickness.