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Evaluating Performance Benefits of Conditioning Formulations on Human Skin
Published in Randy Schueller, Perry Romanowski, Conditioning Agents for Hair and Skin, 2020
Ronald L. Rizer, Monya L. Sigler, David L. Miller
Treatment sites are usually the volar forearm or the lateral aspect of the lower leg. Three to four sites including a no-treatment site can be marked on each arm or leg with a marker and the aid of a template. Usually 2 mg of test material are applied per square centimeter for treatment sites. This has been found to be an effective quantity of a lotion or a cream to sufficiently cover the skin surface (27). Bioinstrumentation measurements are taken at baseline, and at intervals after product application up to 48 hr. The intervals selected depend on effectiveness times required for a claim. For instance, if one wishes to claim that a moisturizer is effective for up to 6 hr, then the results must show a significant difference in moisturization between the 6-hr time point and baseline, and the untreated control site. An untreated control is important to include, since even several hours can affect skin condition, especially if the environmental conditions are changing rapidly. The effectiveness of a moisturizer or a skin barrier repair agent can be assessed using an evaporimeter to measure transepidermal water loss (TEWL), and a conductance meter to measure the relative hydration of the stratum corneum. Both techniques have been shown to be effective in quantifying moisturization treatment effects on skin (28), and typically show an inverse relationship. However, the opposite is true for irritants, which damage the stratum corneum and thus compromise its integrity (Figure 10).
Transdermal Drug Delivery Systems
Published in Ambikanandan Misra, Aliasgar Shahiwala, In-Vitro and In-Vivo Tools in Drug Delivery Research for Optimum Clinical Outcomes, 2018
The visual observation for physical damage is the foremost step in evaluating the integrity of skin preparation. Other methods to check the integrity of the skin barrier include, physical methods, like transepidermal water loss (TEWL), or transcutaneous electrical resistance (TER) (Davies et al. 2004). It has been suggested that before (and in some cases after) the experiment, the integrity of skin barrier should be checked by these methods. The integrity of skin samples may also be checked using the tritium method, where the permeation of triturated water through the skin is determined and compared with standard values (Bartosova and Bajgar 2012).
Methods for Evaluating the Efficacy of Cosmetics Containing Glycerine
Published in Eric Jungermann, Norman O.V. Sonntag, Glycerine, 2018
Transepidermal water loss (TEWL) is defined as insensible water loss through the skin separate and distinct from active perspiration (50). In this technique water flux through the SC is measured, providing a direct measure of the barrier integrity and an indirect assessment of water content. Measurement of TEWL is widely used to assess changes in hydration of the SC (51, 52) and the effect of topically applied moisturizers (53–55), and irritants (41). Its popularity notwithstanding, assessing moisturizer efficacy using TEWL measurements alone has its limitations. This very important point will be discussed at length in this section.
O/W/O multiple emulsions containing soluble collagen: in vitro and in vivo skin biophysical properties evaluation
Published in Journal of Dispersion Science and Technology, 2023
The skin constitutes a barrier that separates environments with deeply different water contents. The barrier properties are ensured by the outermost layer of the skin, the stratum corneum (SC), which controls transepidermal water loss (TEWL).[1] Hydration of corneocytes is provided by the natural moisturizing factor (NMF), which is mainly composed of free amino acids, and various derivatives of these amino acids such as PCA, urocanic acid, and inorganic salts, sugars, as well as lactic acid and urea. The identified inorganic salts include sodium, potassium, calcium, magnesium chlorides, phosphates, and citrates. The NMF is packaged within the corneocytes, accounting for approximately 10% of the corneocyte mass and 20–30% of the dry weight of the stratum corneum.