Trans epidermal water loss

H. Tanojo, H. E. Junginger, and H. E. Bodde, Effects of oleic acid on human trans-epidermal water loss using ethanol or propylene glycol as vehicles, Prediction of Percutaneous Penetration, Vol. 3 (K. R. Brain, V. J. James, K. A. Walters, eds.), STS Publishing, Cardiff, UK, 1993, pp. 319-324. 

Barany E et al. have studied the influence of stearic acid and several stearates, as emulsifiers in eream, on normal as well as on irritated skin [3]. Their results highlighted the possibility of absorption of these emulsifiers into the lipid bilayer, which increased trans-epidermal water loss (TEWL) in normal skin and decreased TEWL in damaged skin. 

In contrast to neat oils, water-based metalwork fluids are the most relevant irritants in the automobile industry. The irritant potential of these fluids depends on their different components, the quality of preventive measures and the continuous care of the fluids. Components with an irritating potential are organic acids, amines, emulsifiers, preservatives, biocides, antifoams and system cleaners. Often, the quality of technical care of the metalwork fluid is inversely proportional to the irritant effect. Actually trans-epidermal water loss (TEWL) measurement offers new chances in the evaluation irritant potential of different metalwork fluids (Hiiner et al. 1994). Figure 1 shows such a TEWL measurement. It was confirmed by an intervention study in a metalwork factory that, in contrast to metalwork fluids A and C, fluid B was not associated with irritant contact dermatitis. The amine component seems to play a relevant role in the irritant potential (Lautenschlager et al. 1997), if the pH value does not exceed pH 9.5. The risk of irritant dermatitis, particularly hand eczema, is closely associated with the duration of exposure. In general, an exposure of less than 2 h per day will not cause an irritant hand eczema... 

Children and particularly babies have a large relative body surface area. Premature babies also have a thinner skin than adults, and lack the outer skin layer known as the homy layer or stratum comeum. In a young child with eczema, the skin may also be more damaged than in an adult with eczema. Therefore, the skin functions less well as barrier. Furthermore, application of any creams or ointments under a nappy or diaper prevents trans-epidermal water loss and leads to an increased absorption of the active substance. 

Emulsion components enter the stratum comeum and other epidermal layers at different rates. Most of the water evaporates, and a residue of emulsifiers, lipids, 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 trans-epidermal water loss (TEWL), the film is identified as occlusive. Application 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 50-75% 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 comeum. 

Mammals are not capable of synthesizing certain unsaturated fatty acids, which ate, nevertheless, fundamental to maintain different functions, snch as the stratum comeum and the skin s barrier function (Pons and Parra, 1995). Linoleic and linolenic fatty acids are considered essential. Linoleic acid is vital for maintaining epidermal thickness and the barrier function that impedes trans-epidermal water loss. A diet lacking in these fatty acids leads to dryness and desquamation, topical application can correct these skin conditions. Linolenic acid gives rise to the prostaglandins and leukotrienes involved in inflammatory processes, which explains why it is applied topically in treatments for sensitive skin. The combination of these two fatty acids is commonly called vitamin F and it is frequently applied topically to improve dryness and dehydration in mature skin. 

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