Corneocytes, size

Histologically, elderly xerotic skin showed an atrophic nucleated epidermis and a threefold increase in corneocyte size. This was accompanied by an approximately 50% increase in the number of... 

Rougier, A. et al. Relationship between skin permeability and corneocyte size according to anatomic site, age, and sex in man, J. Soc. Cosmet. Chem., 39, 15, 1988. 

Corneocytes are about 1 /xm thick and have a mean area of approximately 1000 /xm2. However, the surface area is dependent upon age, anatomical location, and conditions that influence epidermal proliferation such as chemical irritation and UV irradiation.3 Corneocyte size increases with age. This is sometimes assumed to be related to the increased transit time within the SC. On most body sites, the SC consists typically of 12 to 16 layers of flattened corneocytes. 

A number of works investigated the interaction between niosomes and human skin. With niosomes prepared from Ci2 alcohol polyoxyethylene ether and cholesterol, vesicular structures of about 100 nm size have been observed between the first and second layers of human corneocytes 48 h after incubation as well as in the deeper strata of the skin [37], The authors concluded that the structures visualized in the deeper regions could be vesicles reorganized from individual molecules that penetrated the skin. In another study, electron micrographs illustrated that niosomes containing surfactants and cholesterol affected only the most superficial corneocytes. Moreover, two-photon fluorescence microscopy confirmed that fluorescent probe encapsulated in niosomes was confined to the intercellular spaces within the apical stratum corneum layers [56]. 

The effect of age on percutaneous absorption has been examined in vivo in man with variable results. It was postulated (Roskos et al. 1989) that reduced hydration levels and lipid content of older skin may be responsible for a demonstrated reduction in skin permeability where the permeants were hydrophilic in nature (no reduction was seen for model hydrophobic compounds) (Table 14.2). The reduced absorption of benzoic acid demonstrated in the elderly (Rougier 1991) was in line with this suggestion, but not the reduction in absorption of testosterone (lipophilic) (Roskos et al. 1986), or lack of change in the absorption of methyl nicotinate (more hydrophilic) with age (Guy et al. 1983). There are a number of potential physiological changes which may be responsible for age-related alterations, including an increase in the size of individual stratum corneum corneocytes, increased dehydration of the outer layers of the stratum corneum with age, decreased epidermal turnover and decreased microvascular clearance (reviewed in Roskos and Maibach 1992). The issue of age-related variability, however, is far from resolved. 

Marks R. and S. P. Barton, 1983, The Significance of the Size and Shape of Corneocytes, Stratum Comeum, Eds. R. Marks and G. Plewig, Springer, Berlin. 

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