Water loss, transepidermal

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. 

According to results, squalene-including mixtures were able to increase the barrier to maintain hydration in a comparable manner to vernix caseosa. Five percent sodium lauryl sulfate-treated rat and human skin showed increased transepidermal water loss and riboflavin penetration. However, squalene treatment reverts the effects of sodium lauryl sulfate. 

Tupker, R.A., J. Pinnagoda, and J.P. Nater. 1990. The transient and cumulative effect of sodium lauryl sulphate on the epidermal barrier assessed by transepidermal water loss Inter-individual variation. Acta Derm Venereol (Stockh) 70 1. 

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

The process of barrier repair in connection with transepidermal water loss and calcium gradient is illustrated in Figure 6.2. Experiment in mice shows that the calcium gradient disappears after acute permeability barrier disruption, and returns after 6 h in parallel with barrier recovery, barrier... 

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

Results from in vitro experiments, catalytic properties, and tissue localization are all compatible with the role of SCCE in the degradation of intercellular cohesive structures in the stratum corneum as part of the events leading to remodeling of the tissue and eventually to desquamation. Increased expression of SCCE in the epidermis of transgenic mice leads to impaired barrier function with increased transepidermal water loss. The transgenic animals have a thickened epidermis and a marked hyperkeratosis, possibly reflecting compensatory reactions.47-48 There are also other proteases... 

Lavrijsen, A., Oestmann, E., Hermans, J., Bodde, H., Vermeer, B., and Ponec, M., Barrier function parameters in various keratinzation disorders transepidermal water loss and vascular response to hexyl nicotinate, Br. J. Dermatol., 129, 547, 1993. 

Kiistala, R., Lauharanta, J., and Kanerva, L., Transepidermal water loss and sweat gland response in lamellar ichthyosis before and during treatment with etretinate report of three cases, Acta Derm. 

Transepidermal water loss (g/m2/h) was determined with Evaporimeter EP-1 (Servo Med Company, Sweden). Measurements were repeated twice, and the mean was calculated. 

Werner, Y. and Lindberg, M. Transepidermal water loss in dry and clinically normal skin in patients with atopic dermatitis. Acta. Derm. Venereol. (Stockh.) 65 102-105 (1985). 

Kamiya, T., Tsuchiya, S., Hara, K., Okamoto, K., Hattori, A., and Taguchi, N. Study of dry skin in chronic dialysis of skin surface hydration, transepidermal water loss and skin surface structure. Jpn J. 

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. 

Grice, K.A. (1980) Transepidermal water loss in pathologic skin, in The Physiology and Pathophysiology of the Skin, Jarrett, A., Ed., Academic Press, London, pp. 2147-21555. 

Wilhelm, K.P., Cua, A.B., and Maibach, H.I., Skin aging effect on transepidermal water loss, stratum corneum hydration, skin surface pH, and casual sebum content, Arch. Dermatol., 127,1806-1809,1991. 

Brosche, T. and Platt, D., Effect of borage oil consumption on fatty acid metabohsm, transepidermal water loss and skin parameters in elderly people, Arch. Gerontol. Geriatr., 30, 139-150, 2000. 

Despite the well-known clinical coupling of dry skin and itch, studies to objectively compare the degree of skin hydration or measurements of the transepidermal water losses with severity of pruritus have provided conflicting results on this close association. This review will discuss the existing data, breakdown the pathophysiology of xerotic itch, and describe the role of moisturizers in alleviating both entities. 

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. 

Importantly, not all moisturizers provide the same effect in restoration of the barrier function. Certain lipid mixtures or an inadequate concentration of physiologic lipids actually have been demonstrated to inhibit barrier restoration.42,43 Newer ceramide-dominant emollients have been developed in efforts to restore the intrinsic physiologic lipid concentration of the skin. One type of ceramide-dominant emollient was shown to significantly improve the overall severity of atopic dermatitis and demonstrated correction of transepidermal water losses in these patients.44 Unfortunately, studies using ceramide-dominant emollients for patients with atopic dermatitis did not use itch improvement as an endpoint. However, these types of moisturizers likely have a role in the improvement of itch associated with dry skin. 

Eisner, P. and Maibach, H.I., The effect of prolonged drying on transepidermal water loss, capacitance and pH of human vulvar and forearm skin, Acta Derm. Venereol., 70, 105, 1990. 

Aly, R. et al., Effect of prolonged occlusion on the microbial flora, pH, carbon dioxide and transepidermal water loss on human skin, J. Invest. Dermatol., 71,378, 1978. 

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... 

Grice, K., Sattar, H., andBaker, H., Urea and retinoic acid in ichthyosis and their effect on transepidermal water loss and water holding capacity of stratum corneum, Acta Derm. Venereol. (Stockh.), 54, 114, 1973. 

McCallion, R. and Po, A.L.W., Modelling transepidermal water loss under steady-state and non-steady-state relative humidities, Int. J. Pharm., 105, 103, 1994. 

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