Answer:
The histologic and clinical changes following peeling are a direct result of the changes produced in the superficial dermis and epidermis: the removal of the damaged elastotic skin and the reconstruction of this layer with neocollagen after wound healing. Biopsies 48 hrs after phenol peeling demonstrate a keratocoagulation necrosis of the epidermis, extending through the papillary dermis, surrounded by a marked inflammatory reaction.
Epidermal regeneration begins at 48 hours and is usually complete within 7 days. The healed epidermis is no longer in disarray, the cells stain evenly and are uniform in shape, and there is a return of vertical polarity. Melanocytes are present and often of increased density, however they are incapable of synthesizing normal amounts of melanin. The melanocytes of the basilar layer contain fine pigment granules which are evenly dispersed. This reorganization eliminates the tendency to form irregular local pigmentations and lentigines.
The changes within the dermis are profound and contrasts with the adjacent unpeeled dermis. The newly formed matrix consists of compact and parallel bundles of collagen arranged horizontally. There is also an apparent increase in elastic tissue within the papillary dermis resulting in smoother, fuller and more turgid appearance of postpeel skin -- these elastic fibers remain fine and numerous as long as 20 years postpeel. There is a diminution in the presence of ground substance within this dermal band.
Immediately after dermabrasion, the wound serum forms a coagulum across the abraded surface. If allowed to dry, an eschar develops. Beneath this, an intense epithelial proliferation of adnexal elements occurs. Between the third and fifth days, a thin layer of epidermis, lacking rete pegs, has regenerated and there is evidence of re-formed hair follicles and sebaceous glands. This correlated with a thin, shiny red skin beneath the loosening eschar. Epidermal proliferation is complete by day seven and always precedes dermal regeneration. Within the dermis, fibroblasts immediately migrate to the abraded area. In the first two weeks, a considerable amount of collagen is synthesized, forming a horizontal striated pattern similar to that after chemical peeling. Late biopsy of the area shows that the basic architecture is unchanged. Compared to chemical peeling, the histologic changes are more moderate. Dermabrasion does not produce a homogenization of the dermal collagen architecture. There is much less effect on the quantity of pigment present within the basal layer of the epidermis, and there is not the increase in elastic fibers within the dermis. The major change after dermabrasion is a permanent removal of the dermis, which does not regenerate to its original thickness.