Transepidermal water loss 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. 

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. 

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. 

Treatment of xerosis on the plantar surface of the feet for two weeks gave more pronounced improvement in skin roughness, fissures, and dryness by a 40% urea cream (Carmol 40) than from a 12% ammonium lactate lotion (Lac-Hydrin).40 No change in transepidermal water loss (TEWL) was noted from urea-treatment. Both therapies showed sustained benefit during the next two weeks. Furthermore, a cream containing 10% urea and 4% lactic acid provided faster and better improvement with significantly less xerosis regression in patients with diabetes.41... 

Evaluation of the occlusive properties of different pastes in vivo these were evaluated in vivo on tape-stripped skin exactly as described in Reference 10. Briefly, the stratum corneum of the forearm of healthy volunteers was tape stripped until the transepidermal water loss (TEWL) attained values between 40 and 50 g/m2/h. After a rest period of 1 h, 2.5 mg/cm2 of the test products were carefully applied on the stripped sites using a gloved finger, and the TEWL was measured at different times until 120 min after application. Percent changes relative to a nontreated control site were calculated over time. Positive control was white petrolatum. 

Petrolatum s skin moisturization properties are clearly due to its occlusivity,14 and this material is often considered to be the most effective ingredient available for moisturizing dry skin.15 Petrolatum blocks the evaporation of water from the skin (transepidermal water loss TEWL), thus keeping the stratum corneum well hydrated.16 It should be noted that the term moisturization is commonly used to describe the action of occlusive agents on skin, even though water is not actually added to the skin. 

Powers and Fox demonstrated that lanolin is semi-occlusive and can reduce transepidermal water loss (TEWL).36 The application of lanolin and lanolin oil (5.0-6.25 mg/cm2, equivalent to a film thickness of 54-68 /tm) to the inner surface of the forearm reduced the TEWL by 32 and 22%, respectively.36 This is in comparison with petrolatum which reduced the TEWL by 48%. Spruits reported a 20 to 30% reduction in TEWL using a 50-/xm lanolin film.37 The clinical improvement in xerotic skin is not simply due to a transient reduction in TEWL, because a completely impermeable plastic film applied twice a day had no beneficial effects. 

Visible skin dryness has been found to correlate positively with surface hydration, but not necessarily with an increase in transepidermal water loss (TEWL).30 This suggests that significant barrier breakdown is not a requirement for skin dryness. A continued increase in dryness to values above a certain level may, however, lead to scaling, cracking and chapping, barrier breakdown, and, eventually, to irritation. 

Loden, M., Olsson, H., Axell, T., and Linde, Y.W., Friction, capacitance and transepidermal water loss (TEWL) in dry atopic and normal skin, Br. J. Dermatol., 1992 126 137-141. 

Measurement of the transepidermal water loss (TEWL) is the standard method to determine SC barrier status. A disturbed skin barrier is characterized by high TEWL.7 The measurement of the TEWL is based on the diffusion principle in an open chamber. The density gradient is measured... 

Hydration measurements with various electrical devices30 Laser Doppler imaging30 Transepidermal water loss (TEWL)... 

Pinnagoda, J., Tupker, R.A., Agner, T., and Serup, J., Guidelines for transepidermal water loss (TEWL) measurement, Contact Dermatitis, 22, 164, 1990. 

Transepidermal water loss (TEWL) L skin reflectance a red/green axis b blue/yellow axis Skin blood flow... 

Transepidermal water loss (TEWL) is a natural occurrence that takes place in the skin layers. TEWL is the result of movement of water from the deep skin layers across the epidermis into the outside atmosphere. It is a tightly regulated process that is controlled by the stratum comeum [9], Occlusive topical bases and devices, such as transdermal patches, block TEWL and cause increased hydration of the skin. Hydration of the skin increases the permeation rates of compounds transdermally. The occluding effect of transdermal patches is an important mechanism that promotes increased diffusion of the compound across the skin into the systemic circulation [10]. 

The bismuth subgallate powder comes away from the skin automatically (figure 36.14) with the Vaseline that prevents transepidermal water loss (TEWL) evaporation. The downtime is 8-10 days maximum. 

T Agner, J Serup. Time course of occlusive effects on skin evaluated by measurement of transepidermal water loss (TEWL). Contact Dermatitis 28 6-9, 1993. 

A short-term test that measures transepidermal water loss (TEWL) is also used to measme barrier integrity and has been mentioned specifically as an acceptable method by the Emopean Union s Scientific Committee for Cosmetics and Non-Food Products (Scientific Committee, 2003). Measinement of TEWL from skin samples in diffusion cells appears to be a potentially convenient method that does not use radiolabeled material. However, some effort appears to be necessary to obtain consistent measmements, including the possible need for rooms with controlled environments for humidity and temperature (Benech-Kieffer et al., 1998). Some reports have found differences between skin permeability evaluations by tritiated water and TEWL methods (Chilcott et al., 2002). 

Transepidermal water loss (TEWL) can be considered a determinant indicative of the functional state of the cutaneous barrier (Wilson and Maibach, 1982 Maibach et al., 1984 Rougier et al., 1989) and provides a method for assessing macroscopic changes in the barrier properties of the SC (Abrams etal., 1993). Biophysical investigations suggest that the SC lipid domains are the primary barrier to both water loss and the penetration of compounds through the skin (Van Duzee, 1971 Kalia etal., 2001). Therefore, measurement of TEWL is a relevant parameter for the... 

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