Time- and site-dependent differences in epidermal barrier properties were investigated over the first 28 days of life in healthy term newborn infants. Diapered and nondiapered skin sites were contrasted to the volar forearm of adults (mothers). Thirty-one term infants were evaluated in the hospital on postnatal day 1 and at home on days 4, 7, 14, 21, and 28 for a total of six visits. Measurements included baseline skin hydration, continuous capacitive reactance, peak water sorption, rate of water desorption, skin pH, skin temperature, and environmental conditions. Changes in epidermal barrier properties over the first 4 weeks of life included an increase in surface hydration, a decrease in transepidermal water movement under occlusion, a decrease in surface water desorption rate, and a decrease in surface pH. Diapered and nondiapered regions were indistinguishable at birth but exhibited differential behavior over the first 14 days, with the diapered region showing a higher pH and increased hydration. Maternal measurements remained constant throughout the period. We conclude that healthy newborn skin undergoes progressive changes in epidermal barrier properties over the first 28 days. Adult skin testing does not replicate newborn skin during the first month of life.

OBJECTIVES:To characterize vernix caseosa in newborn infants with respect to factors that influence vernix distribution on the skin surface, vernix effects on thermal stability, skin hydration, acid mantle development, and vernix antioxidant properties. STUDY DESIGN:Vernix distribution was determined for 430 infants. Thermal stability was assessed in parallel groups following vernix retention (n ¼ 66) and removal (n ¼ 64). The effects of vernix retention on skin hydration, pH, erythema, and dryness/scaling were determined. Samples were analyzed for vitamin E before and after UV exposure. RESULTS:Vernix distribution depended upon gestational age, delivery mode, gender, race, and meconium exposure. Retention had no effect on axillary temperatures. Skin hydration was significantly higher for vernix-retained skin. Skin pH and erythema were significantly lower with retention. Vitamin E levels were decreased by ultraviolet radiation. CONCLUSIONS:Vernix is a naturally occurring barrier cream with multiple salubrious effects, which support its retention on the skin surface at birth.

Recent studies have prompted interest in the use of epidermal barrier creams as protective biofilms for very low birthweight preterm infants. The key to understanding the role of epidermal barrier films is an elucidation of their interaction with water and a basic knowledge of their composition. In this study, we investigated the morphologic properties and elemental composition of the naturally occurring biofilm, vernix caseosa. This biofilm is typically lacking in preterm infants and its production coincides in utero with terminal differentiation of the epidermis and formation of the stratum corneum. Significantly, vernix (80.5+/-1.0% H2O) had a much higher water content than other barrier creams (Eucerin: 17.1+/-0.6%, Aquaphor: 0.33+/-0.03%, Ilex: 0.19+/-0.02%, petrolatum: 0.03+/-0.01%; all p<0.05). Phase contrast microscopy of vernix showed multiple cellular elements with nucleic "ghosts" embedded in a putative lipid matrix. Transmission electron microscopy revealed flattened structures approximately 1-2 microm in thickness with distinct cellular envelopes indicative of differentiated corneocytes. Compared with mature corneocytes in adult stratum corneum, vernix corneocytes appeared swollen, the density of the keratin filaments was less, and there was a relative lack of tonofilament orientation. Cryofractured specimens were examined by cryoscanning electron microscopy with subsequent elemental localization by X-ray beam analysis. The findings indicate the high water content of vernix is largely compartmentalized within fetal corneocytes. These results are consistent with the novel view of vernix as a "fluid phase" stratum corneum consisting of a hydrophobic lipid matrix with embedded fetal corneocytes possessing unique biomechanical and water-binding properties.

Detailed models of solute transport through the stratum corneum (SC) require an interpretation of apparent bulk diffusion coefficients in terms of microscopic transport properties. Modern microscopy techniques provide a tool for evaluating one key property-lipid pathway tortuosity-in more detail than previously possible. Microscopic lipid pathway measurements on alkali expanded human SC stained with the lipid-soluble dyes methylene blue, Nile red, and oil red O are described. Brightfield, differential interference contrast, fluorescence, and laser scanning confocal optics were employed to obtain 2-dimensional (2-D) and 3-dimensional (3-D) images. The 2-D techniques clearly outlined the corneocytes. Confocal microscopy using Nile red yielded a well-delineated 3-D structure of expanded SC. Quantitative assessment of the 2-D images from a small number of expanded SC samples led to an average value of 3.7 for the ratio of the shortest lipid-continuous pathway to the width of the membrane. This was corrected for the effect of alkaline expansion to arrive at an average value of 12.7 for the same ratio prior to swelling.

Restoration of an epidermal barrier is a definitive requirement for wound closure. To determine formation of an epidermal barrier as a function of hydration of the stratum corneum, we measured surface electrical capacitance (SEC) of the epidermis in cultured skin substitutes (CSS) in vitro and after grafting to athymic mice. CSS were prepared from human keratinocytes and fibroblasts attached to collagen-glycosaminoglycan substrates. On culture days 3, 7, 14, 17, and 21, SEC was measured in situ. CSS (n = 18; mean +/- SEM) showed a time-dependent decrease of SEC (picoFarads, "pF") from 4721 +/- 28 pF on day 3 to 394 +/- 117 pF on day 14, and subsequent increase to 1677 +/- 325 pF on day 21. After 14-d incubation, parallel CSS samples (n = 5) or murine autografts (n = 5) were grafted orthotopically to athymic mice. After grafting, CSS showed decreases in SEC from 910 +/- 315 pF at 2 wk to 40 +/- 10 pF at 4 wk with no significant decreases thereafter. Control values for murine autograft were 870 +/- 245 pF at 2 wk, and 87 +/- 30 pF at 4 wk. SEC values for native murine skin (n = 10) were 91 +/- 18 pF, and for native human skin (n = 10) were 32 +/- 5 pF. The data demonstrate that SEC decreases with time in culture and that healed or intact skin has approximately 10- to 100-fold lower SEC than CSS in vitro. This noninvasive technique provides a quantitative index of epidermal barrier in CSS in vitro and demonstrates the development of functional epidermal barrier during healing of wounds treated with cultured skin substitutes.