Epidermal thickening

Kang et al. [23] compared the clinical, histologic, and molecular responses of normal human skin to topical retinol with that of retinoic acid. Application of retinol and retinoic acid produced epidermal thickening. However, retinol produced less erythema compared with retinoic acid. The authors suggest that these data are compatible with the idea that retinol may he a pro-hormone of retinoic acid. 

In the elegant studies by Zhou and coworkers, simultaneous overexpression of catalytically active uPA and uPAR in keratinocytes in the presence of plasminogen resulted in a pathological phenotype of the skin characterized by extensive alopecia, induced by involution of the hair follicles, epidermal thickening, and subepidermal blisters [4,68]. No skin phenotype was evident in mice with targeted overexpression of either uPA or uPAR alone, of catalytically inactive uPA together with uPAR, or in the absence of plasminogen. 

Soldiers, by the nature of their profession, are at increased risk of mechanical skin damage. Friction blisters of the extremities are common (Hoeffler 1975) Knapik et al. (1992) reported that 69% of 335 soldiers participating in a maximal-effort road march developed foot blisters. Chronic or intermittent low-intensity irritation induces epidermal thickening, and strong acids (sulfuric, hydrochloric) and alkalis may cause chemical cauterization on contact with the skin (Shaposhnikov 1973 Naidenov 1980). 

Other examples of the cytological effects of surfactants have been reported in papers dealing with cell proliferation. Tween 60 brings about a rapid and sustained intensification of cell proliferation following application as a 10% solution to the epidermis [193] there is rapid and sustained epidermal thickening accompanied by an increase in the thymidine-labelling index. Three surfactants have been studied as modulators of transformed cell proliferation [194]. Some surface active compounds have both in vitro and in vivo antitumour activity, and others inhibit the development of tumour metastases in vivo. Lack of in vivo effect... 

The reason for the observed increase in lipid labelling is not immediately obvious. None of the biopsies taken for histology showed evidence of epidermal thickening, and so the results cannot be explained in terms of an increased mass of viable tissue per unit area of epidermis. The use of a labelled precursor in substrate, rather than tracer, quantities, makes it unlikely that the finding is an artifact caused by changes in metabolic pool sizes. Nor does it seem possible to account for the results in terms of increased cell turnover, as the rate of epidermal proliferation in both autosomal dominant and sex-linked recessive ichthyosis is within normal limits . Whether lipid turnover is... 

Two biopsies were performed for evaluation of the light microscope appearance of formalin fixed paraffin wax embedded tissue. They both showed some epidermal thickening and concentric lamellae of stratum corneum within the follicular ostia (Figure 16.6). There were no other changes of note. 

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