TEWL

Emulsion components enter the stratum corneum and other epidermal layers at different rates. Most of the water evaporates, and a residue of emulsifiers, Hpids, and other nonvolatile constituents remains on the skin. Some of these materials and other product ingredients may permeate the skin others remain on the surface. If the blend of nonvolatiles materially reduces the evaporative loss of water from the skin, known as the transepidermal water loss (TEWL), the film is identified as occlusive. AppHcation of a layer of petrolatum to normal skin can reduce the TEWL, which is normally about 4—8 g/(m h), by as much as 50 to 75% for several hours. The evaporated water is to a large extent trapped under the occlusive layer hydrating or moisturizing the dead cells of the stratum corneum. The flexibiHty of isolated stratum corneum is dependent on the presence of water dry stratum corneum is britde and difficult to stretch or bend. Thus, any increase in the water content of skin is beHeved to improve the skin quaHty. 

Here the TEWL-value measurements showed that Kujalnik peloids and magnesium pelobischofite complex salutary potentize each other in their mixtures and provide the effective preservation of acidic mantle of the skin. Besides, the pelobischofite addition to the cosmetic cream compositions results in the effective coverlet moistening. Also, the pelobischofite addition provides the decrease of the negative surfactants effect on the skin health. The TWL parameter value is less by half, the water balance of the skin is normalized and the wrinkled skin becomes smoothed out and velvety. 

Recently Blake et al.153) made such studies in the case of human (HL) and tortoise egg-white (TEWL) lysozyme based on crystallographic refinements at 1,5 and 1,6 A resolution, respectively. By these investigations they attempted to obtain information on the perturbations of water structure in the hydration shell by neighboured protein molecules and by high salt concentrations as well as on the degree of order of the bound water. The authors came to the conclusion that the number of ordered water molecules are 128 in TEWL and 140 in HL, whereas the overall content is made up of 650 and 350 water molecules per lysozyme molecule. 

TEWL), a measure of damage to the stratum comeum, also increased after exposure to JP-8 [34,35,38,39]. 

F. Netzlaff, K.-H. Kostka, C.-M. Lehr, and U. F. Schaefer. TEWL measurements as a routine method for evaluating the integrity of epidermis sheets in static Franz type diffusion cells in vitro. Limitations shown by transport data testing. Em J. Pharm. Biopharm. 63 44—50 (2006). 

Barrier Integrity (Relative TEWL) Passive Iontophoresis... 

Relative TEWL indicates the value of transepidermal water loss across the compromised skin barriers relative to that of normal, intact skin. 

Several classes of ceramides have been described in human skin.14 Today it is considered that the ceramides are essential for the barrier properties. It has been suggested that the lower amount of ceramides found in stratum corneum in atopic dermatitis26,27 explains the increased TEWL seen in dry atopic skin. In this context it is of special interest to note that part of the long-chain ceramides of the horny layer are covalently bound to the proteins forming the corneocyte envelope.25 This suggests that such lipids constitute anchors of the hydrophobic phase to the corneocytes and thereby add to the cohesion of the cells of the horny layer. 

From these requirements we may infer a structure where the bulk of the intercellular lipids exist in the crystalline, close-packed state in stacked bilayer structures (Figure 2.5) due to the large amounts of long-chain saturated species. However, circumstantial evidence, for example, TEWL, indicates that a fraction of the lipid compartment should be in the liquid crystalline state, but as yet we do not know the composition of this fraction. Again the role of cholesterol may be crucial, as mentioned earlier. 

FIGURE 6.2 Illustration of skin barrier repair in epidermis. SC, stratum corneum SG, stratum granulosum TEWL, transepidermal water loss ELS, epidermal lipid synthesis. 

On the other hand, although dry skin or skin itchiness has frequently been recognized together with pigmentation in the patients with chronic kidney failure and receiving HD,9 only a few reports have been made on the characteristics of dry skin (e.g., high pH,10 decrease of water content in SC, and low TEWL.11)... 

The TEWL in both regions was three to four times higher in AD patients than in the control (Figure 9.2), and the lesional skin gave higher values than the nonlesional skin (p < 0.05). On the other hand, the TEWL was only slightly higher in HD patients than in the control (mean value HD patients, 7.0 g/m2/h, the control, 5.0 g/m2/h). The barrier function of SC in HD patients was similar to that in the control. 

The characteristics of hydration level and barrier function of SC in various types of dry skin were reviewed and summarized in Table 9.3. They are senile xerosis, seasonal allergic rhinitis, ichthyosis valgaris, and experimentally induced dry skin including atopic xerosis and dry skin by hemodialysis. The water content decreased in every type of dry skin and the free amino acids content also decreased corresponding to the decrease of the water content. However, the TEWL or the ceramide levels showed no clear tendency throughout every type of dry skin, especially ceramides showed higher or lower value even though the water content in SC was consistently lower in every type of dry skin. 

The water content in SC was low both in AD and HD patients, and their skin was obviously dry. However, there was a great difference between them in TEWL. The TEWL was high in AD patients accompanied with extremely inferior barrier function of SC, while HD patients showed a slightly higher TEWL than the controls and their barrier function proved to be in the mostly normal range. The findings obtained in HD patients resembled the symptoms of senile xerosis20,21 and coincided with those reported by Kamiya et al.11 The difference in TEWL between AD and HD patients and the... 

A significant difference was found only in TEWL between the lesional and nonlesional skin of AD patients. However, all the measurements on the nonlesional skin, except for skin surface pH, gave values intermediate between those on the lesional skin and those in the controls. 

Dry, scaly skin is characterized by a decrease in the water retention capacity of the stratum corneum (SC),1 with water content diminished to less than 10%. Barrier function of the SC is usually declined, and transepidermal water loss (TEWL) is increased because of an abnormality on barrier homeostasis.2 People feel tightness of their skin, and the skin surface becomes rough, scaly, and sensitive. Hyperkeratosis, abnormal scaling, and epidermal hyperplasia are usually observed in the dry skin.2 Keratinization also shows abnormal features.2 These phenomena are commonly observed in atopic dermatitis and psoriasis.3 Dermatitis induced by environmental factors such as exposure to chemicals, low humidity, and UV radiation also shows these features. Thus, many researchers have been investigating the cause and treatment of dry skin, and there is currently great interest in adequate model systems for dry skin studies. In this chapter, I will describe several model systems of dry skin for clinical research of dermatitis associated with skin surface dryness and also mention recent studies to improve the dry skin. 

Previously13 investigators usually used back or forearm skin for the experiment. It was easier to induce scaly skin on back skin than on forearm skin. In the case of back skin, we stripped SC nine times with adhesive cellophane tape. At that time, the transepidermal water loss (TEWL) value was over 10 mg/cm2/h and most of the SC was removed. In the case of forearm, to induce dry, scaly skin, stripping for 30 to 50 times was needed. One week after treatment, TEWL was higher than the normal level, skin surface conductance decreased, and SC cell area also decreased (Table 10.1). The skin surface became scaly and flaky. Figure 10.1 shows skin surface pictures of the forearm skin with and without barrier disruption. Abnormal scaling is observed on the surface of skin, which was treated with tape stripping. These phenomena are commonly observed in natural dry skin, such as atopic dermatitis and psoriasis. 

The effect of a surfactant on skin depends on the type of surfactant as described earlier. Wilhelm et al. demonstrated the irritation potential of anionic surfactants.21 They evaluated the effects of sodium salts of n-alkyl sulfates with variable carbon chain length on TEWL and found that a C12 analog gave a maximum response. They suggested that the mechanisms responsible for the hydration of SC are related to the irritation properties of the surfactants. Leveque et al. also suggested22 that the hyperhydration of SC is consecutive to the inflammation process. They demonstrated that the increase of TEWL was induced by SDS without removal of SC lipids. SDS might influence not only SC barrier function, but also the nucleated layer of epidermis and dermal system associated with inflammation.23 Recently, no correlation was found between the level of epidermal hyperplasia and TEWL increase on the SDS-irritated skin.23 Further work would be needed to determine the effects of surfactants on skin. 

Welzel, J., Metker, C., Wolff, H., and Wilhelm, K.P. (1998) SLS-irritated human skin shows no correlation between degree of proliferation and TEWL increase. Arch. Dermatol. Res. 290 615-620. 

Atopic dermatitis is the most common itchy dermatosis, with well-documented alteration in the stratum comeum function. Numerous studies have revealed an increase in the basal transepidermal water loss (TEWL) in the stratum corneum of patients with this condition. Of note, this increase in TEWL was also described in the clinically unaffected skin of atopies.2 There have been direct correlations shown between the degree of inflammation and severity of barrier impairment in atopic dermatitis. Despite these findings, to date there have been no definitive reports correlating degree of barrier function with itch variability. 

Seidenari, S. and Giusti, G. Objective assessment of the skin of children affected by atopic dermatitis a study of pH, capacitance and TEWL in eczematous and clinically uninvolved skin. Acta. Derm. Venereol. 75, 429-433 (1995). 

Dithranol in combination with urea is widely used in psoriasis to improve the clinical efficacy, to minimize the dithranol concentration, to achieve the desired effect, to shorten the contact, to get a better hydration of the stratum corneum, and to decrease the proliferation rate of the keratinocytes. Gabard and Bieli showed an increased keratolytical effect of salicylic acid by adding 10% urea.54 Hagemann and Proksch55 showed in 10 patients with psoriasis under a 2-week treatment with a 10% urea ointment increased stratum corneum hydration, a small decrease in TEWL, a reduction in epidermal thickness (-29%), and a decreased epidermal proliferation (-51%). The altered expression of involucrin and cytokeratins as marker for epidermal proliferation was partially reversed.55... 

With topically applied 10% urea ointment, Sasaki et al. showed an improvement of stratum corneum water content, hygroscopicity, and TEWL, in psoriasic patients.56... 

In an own controlled study we treated 12 psoriatic patients with a glycolic acid lotion 15% versus a 0.05% betamethasone valerate cream.63 TEWL (Evaporimeter EP1, ServoMed, Sweden), Laser Doppler (Perimed-Periflux, Sweden), and skin color (Chroma Meter CR-200, Minolta, Japan) were taken at baseline and on day 5-10-15 on psoriatic lesions. Erythema a value was used for monitoring. The results of the study showed that ... 

The TEWL values decreased significantly within 15 days on both sites, particularly for the corticosteroid treated site (P <. 01 glycolic, P <. 005 betamethasone). However, no significant differences in TEWL between glycolic acid and betamethasone could be detected. 

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