To estimate the differentiation speed of the corneocytes, we suggest using their flatness index rather than the two-dimensional cell surface area, because the former is a concept that takes into account the three-dimensional characteristics of corneocytes.

Three Corneometer instruments evaluated in this study gave close measurements and correlated well. Nevertheless, pretest validation of instruments should be undertaken in multicenter studies where capacitance data are compared or pooled, and concordance among instruments should be documented prior to study.

Because of the presence of thick long hairs on the scalp, little information is available concerning the functional characteristics of the stratum corneum (SC) of scalp skin. We therefore conducted a functional study of the SC of lesional scalp skin of patients with alopecia areata and of patients with androgenetic alopecia. We compared the scalp with the cheek and the flexor surface of the forearm (volar forearm). The water barrier function of the scalp SC of both patient groups, in terms of transepidermal water loss (TEWL), was almost comparable to that of the volar forearm, and was far better than that of facial skin. However, hydration of the scalp skin surface, as evaluated by measurement of high-frequency conductance, was markedly higher than that of facial skin, and showed significantly higher values than the volar forearm. These characteristics seem to be dependent, at least to some extent, on the amount of sebum-derived skin surface lipids because these were abundant on the scalp skin. Moreover, removal of skin surface lipids led to a significant decrease in skin surface hydration. The superficial corneocytes, the size of which reflects the proliferative activity of the epidermis, were substantially smaller on the scalp than on the volar forearm but significantly larger than on the cheek. These findings suggest that the rate of turnover of the scalp epidermis is intermediate between that of the facial and volar forearm epidermis. We conclude that the SC of the scalp skin in humans is functionally distinct from that of the face and extremities.

Background/purpose: Epicutaneous labeling or intradermal injection of the fluorescent sodium fluorescein is being used increasingly to investigate skin conditions in vivo when using non‐invasive devices such as confocal scanning laser microscopy. Sodium fluorescein was used intravenously for decades for the examination of the vasculature of the ocular fundus (fluorescein angiography) and as eye drops for diagnosis of corneal erosions. The objective of this article is to systematically review the literature on fluorescein and conclude its safety in cutaneous research to support research planning and evaluations by ethics committees. Methods: A number of databases and the literature about safety and toxicity of fluorescein in animal and human studies were searched and analyzed. Results: Side effects or adverse events reported in the literature were related to intravenous bolus injection. Transient nausea and vomiting may occur. Other adverse events such as vasovagal reaction, cardiac or respiratory effects and anaphylaxes are extremely rare but may be fatal. Intradermal injection may cause mild itch or pain; systemic adverse event was reported. Epicutaneous labeling is associated with no reported problem. A typical local dose is several magnitudes of order smaller than a typical intravenous dose. Conclusion: Fluorescein has been used for many years in medicine for diagnostic purposes and is widely safe, albeit intravenous bolus injection may cause serious adverse reactions. In the literature, we could not trace reports of local or systemic side effects of topical sodium fluorescein except itch and pain on intradermal injection, however, dependent on the fluorescein preparation used. Local dermal application of fluorescein for in vivo study of skin may be considered widely safe.

The subtle dryness of the skin surrounding the lesions of atopic dermatitis (AD) is called atopic dry skin or atopic xerosis (AX). AX is more susceptible to the development of AD skin lesions under various environmental stimuli than the clinically normal skin of the people who have or have had or will have AD, which might be called normal atopic skin (NAS) that shows no functional differences as compared to the skin of normal individuals. Routine histopathologic studies of AX that involve the invasive procedures of biopsy are not so helpful in clarifying the underlying pathogenesis. Modern, noninvasive biophysical instrumentation provides rich and quantitative information about various functional aspects of skin. The stratum corneum (SC) of AX reveals not only decreased hydration but also mildly impaired barrier function demonstrable as an increase in transepidermal water loss, elevated pH values, and an increased turnover rate of the SC consisting of thick layers of smaller-sized corneocytes. These data suggest that AX is related to mildly increased epidermal proliferation as a result of the presence of subclinical cutaneous inflammation. Although AX skin does not display any impairment in the recovery of barrier function after physical skin irritation by tape-stripping, it produces a much more severe, long-lasting inflammatory response together with a delay in barrier repair after chemical irritation such as that induced by sodium lauryl sulphate. The SC of AX is biochemically characterized by reduction in the amounts of ceramides, especially ceramide I, sebum lipids, and water-soluble amino acids. None of these changes in SC functions are seen in NAS, which includes not only the normal-looking skin of AD patients long after regression of all active lesions but also of latent atopic skin such as neonates who later develop AD. This suggests that all of the observed functional as well as biochemical abnormalities of AX are a reflection of subclinical inflammation. The presence of the underlying inflammation in AX also differentiates it from senile xerosis. The mildly impaired SC functions of AX can be improved by daily repeated applications of effective moisturizers, i.e., corneotherapy, which is effective in preventing the exacerbating progression of AX to AD resulting from inadvertent scratching of the skin that facilitates the penetration of environmental allergens into the skin. The biophysical confirmation of such efficacy of moisturizers, including cosmetic bases on the mildly impaired barrier function and decreased water-holding capacity of the SC of AX, definitely substantiates the importance of skin care for the cosmetic skin problems that affect every individual in the cold and dry season ranging from late autumn to early spring.