The barrier component and the driving force component of transepidermal water loss and their application to skin irritant tests.

BACKGROUND/AIM: According to Fick's law of diffusion, the rate of transepidermal water loss (TEWL) is determined by a barrier component and a driving force component. The objective of this study is to propose novel indicators for the assessment of skin irritation potential from chemicals using these components. METHODS: Before and after acetone/ether (AE), sodium lauryl sulfate (SLS) and nicotinic acid methyl ester (NME) treatments, the apparent mass transfer coefficient of water, K, of the stratum corneum (SC) and the apparent water vapor pressure, P(d), at the interface between SC and epidermis were estimated as measures of the SC barrier and the driving force, respectively. RESULTS: After AE treatment, K showed marked increase and P(d) remained approximately constant. All participants reacted to NME with erythema and the laser-Doppler flowmetry (LDF) value peaked at around 30 min. While there was a change in P(d), which parallels with LDF changes, K showed little variation. Repeated SLS treatment induced a slight increase in P(d) besides an increase in K. In the meantime, all participants reacted with subtle erythema. CONCLUSIONS: Our results suggest that not only the SC barrier but also the driving force determines variations in the TEWL rates during skin irritant tests. Together, K and P(d) will provide us with invaluable information about skin condition.

Tear evaporation dynamics in normal subjects and subjects with obstructive meibomian gland dysfunction.

PURPOSE: To test a newly developed tear evaporimetry system that detects real-time changes in tear evaporation rates and shows the tear film stability in patients with obstructive meibomian gland dysfunction (MGD). METHODS: A ventilated chamber system with high-sensitivity microbalance sensor was used to evaluate tear evaporation. Tear evaporation rates and dynamic changes in them in response to blinking ("flip heights") were measured. Both were compared in 38 eyes of 22 normal subjects and 32 eyes of 21 patients with obstructive MGD, in a prospective case-control study. The relationship between tear evaporation rates and flip heights to meibomian gland orifice obstruction was also analyzed. RESULTS: Changes in tear evaporation rates produced by blinking were detected. The tear evaporation rates in the patients' group were 5.8 +/- 2.7(10(-7)) g/cm(2) per second, significantly higher than in normal subjects (4.1 +/- 1.4[10(-7)] g/cm(2) per second; P = 0.0008). The flip heights in the obstructive MGD group were 0.58 +/- 0.33(10(-7)) g/cm(2) per second, significantly higher than in normal subjects (0.39 +/- 0.27[10(-7)] g/cm(2) per second, P = 0.02). The correlations between both tear evaporation rates and flip heights to the meibomian gland orifice obstruction score were statistically significant (P < 0.0001 and P = 0.004, respectively). CONCLUSIONS: This new system was helpful in differentiating MGD patients from normal subjects. These significantly higher evaporation rates and higher flip heights reflect the unstable tear evaporation and may well indicate unstable tear film in patients with obstructive MGD with abnormal evaporative tear loss.

Assessment of epidermal barrier function by photoacoustic spectrometry in relation to its importance in the pathogenesis of atopic dermatitis.

With the use of the photoacoustic spectrometry system, in which a mixture of lipid- and water-soluble dyes is applied to the skin and then irradiated with light from a xenon lamp (425 nm and 550 nm), we measured photoacoustic signals of both dyes within the stratum corneum and their disappearance rate through the stratum corneum. The signal intensity was higher and dyes penetrated faster in clinically normal skin of patients with atopic dermatitis (AD) compared with healthy subjects, indicating an impairment of the in vivo cutaneous permeability barrier function against both lipophilic and hydrophilic chemicals. Furthermore, penetration rates of the hydrophilic dyes tended to increase in proportion to the severity of AD and significantly correlated with serum IgE levels in the severe AD group. Thus, abnormal barrier functions of clinically normal skin in AD may predispose inflammatory processes evoked by irritants and allergens, especially their water-soluble elements.