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

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.