The Predilection Sites for Chronic Atopic Dermatitis Do Not Show Any Special Functional Uniqueness of the Stratum corneum

Abstract

The functional deficiencies of the stratum corneum (SC) have been well documented in the skin of atopic dermatitis (AD) patients. AD tends to affect certain predilection areas chronically such as the face, neck and the flexural folds of the extremities. From the paucity of the information about the functional characteristics of the SC in such skin areas, we conducted biophysical measurements at the predilection sites of AD, i.e. the cheek, anterior surface of the neck, nape, antecubital fossa and popliteal fossa and relatively uninvolved sites such as the elbow, mid volar forearm, knee and mid calf in 34 AD patients and in 40 normal individuals. Reflecting the great interlocation variations in the SC noted even in the normal individuals, we found location-dependent as well as severity-dependent changes of SC function in the AD patients. Thus, the values of transepidermal water loss (TEWL) obtained on the cheek and, unexpectedly, the elbow were quite high, whereas those on the poplieal fossa were very low; even those values recorded on the lesional skin of the latter of the AD patients were significantly lower than those of the cheek of normal healthy individuals (p < 0.05). Moreover, the TEWL values measured at the nonlesional skin of AD patients were much closer to those of the normal healthy skin than to those of the lesional skin in most areas. Similarly, the SC hydration state that is influenced by the amount of skin surface lipids showed prominent location-dependent changes in addition to a severity-dependent change. It was much higher even in the lesional skin of the face and neck than in the normal skin of the extensor surface of the limbs. The corneocyte size, which inversely correlates with the turnover rate of the SC, was larger even on the lesional skin of the extremities than that of the normal cheek. It is only in skin surface pH that such location dependency was not demonstrable; it uniformly revealed higher values in the lesional and nonlesional skin of AD patients regardless of the sites. From these comparative data obtained at the predilection sites and relatively unaffected sites of AD, we think that those functional abnormalities of the SC reported in AD patients simply reflect the severity of underlying inflammatory changes rather than inherently defective SC functions.

Location‐related differences in structure and function of the stratum corneum with special emphasis on those of the facial skin

“…However, even on the normal skin, in vivo measurement of TEWL clearly demonstrates great variations between different body regions reflecting the differences in thickness as well as the degree of the structural integrity because of maturity of the SC. Thus, the TEWL values measured on the facial skin is more than 10 g m )2 h )1 , being much higher than those of the forearm and upper arm whose TEWL is around 5 g m )2 h )1 similar to those measured on the trunk and lower extremity [10,11]. Likewise, that measured on the scalp [12] or on the axilla [13] is around 7 g m )2 h )1 , whereas that on the female vulva reaches 25 g m )2 h )1 , because the SC of the genital skin is the thinnest on the body as mentioned above [2,14].…”

“…In contrast, the skin of the knee covering another highly movable joint does not show any such high TEWL values. Likewise, the antecubital fossa or the popliteal fossa, the flexor surfaces of the joint regions, does not show any specifically higher TEWL than other sites of the extremities, although they constitute one of the predilection sites for atopic dermatitis like the neck [10]. From such findings, it is hard to speculate that the SC barrier deficiency of this range is the major factor facilitating the development of the skin lesions of atopic dermatitis.…”

“…Various types of skin lesions covered by pathological SC always reveal higher TEWL because of impaired barrier function [6,9,10]. However, even on the normal skin, in vivo measurement of TEWL clearly demonstrates great variations between different body regions reflecting the differences in thickness as well as the degree of the structural integrity because of maturity of the SC.…”

“…As mentioned above, TEWL, which takes place between the water-saturated living epidermis and dry environmental atmosphere through the SC under non-sweating condition, namely at the ambient condition of around 20°C and 40-50% relative humidity, can be used as an endogenous standard for the SC barrier function. Various types of skin lesions covered by pathological SC always reveal higher TEWL because of impaired barrier function [6,9,10]. However, even on the normal skin, in vivo measurement of TEWL clearly demonstrates great variations between different body regions reflecting the differences in thickness as well as the degree of the structural integrity because of maturity of the SC.…”

“…Although the barrier function of the SC plays a vital role in enabling our terrestrial existence, we can live without any inconvenience as long as the TEWL is near the level of the normal genital skin that is covered by extremely thin SC whose TEWL is comparable to that of severe inflamed skin of atopic dermatitis present on the trunk and limbs [10,14]. Even when we totally remove the SC of the volar forearm by tape-stripping to induce a barrier-impaired area, its barrier function can be quickly repaired to attain such TEWL levels within 3 days by the rapid production of incompletely composed SC equipped with sufficient levels of the intercellular lipids either in healthy individuals or in patients with atopic dermatitis [29,30].…”