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Skin Care Moisturizers
By: Eric S. Abrutyn, TPC2 Advisors Ltd., Inc.
Posted: November 30, 2010, from the December 2010 issue of Cosmetics & Toiletries.
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TEWL: TEWL measures the occlusivity of water on skin as it migrates to the surface.12, 13 Healthy skin will have low TEWL while damaged skin will have high TEWL. Occlusive films such as petrolatum can disguise the real health of skin because they create an occlusive barrier and reduce the ability to predict the actual transpiration rate of moisture evaporation from the SC. TEWL reduction lasting for several hours, i.e. from 4–24 hr after application of a moisturizer, can be used to predict the ability of the formulation to reduce water loss from the SC. Thus, when a product applied to skin shows prolonged TEWL reduction, this measurement can infer the product’s ability to reduce water loss from the skin. Instruments used for the measurement of TEWL include evaporimeters and TEWL probes operating on vapor pressure gradient open chamber principles.
Conductance: Conductance14, 15 uses the Galvanic skin response to measure electrical charges in the skin. These charges relate to the water-binding capacity of the SC.
Corneometry: Corneometry16, 17 is a capacitance measurement based on changes in the dielectric constant due to variations in skin surface hydration. Water and other materials on the skin’s surface will have a different capacitance reading. Measurement comparisons using this method are limited to in-study comparisons.
Observer dryness: Observer dryness assesses skin health through subjective, trained clinician grading. This is usually conducted in conjunction with panelist dryness grading (e.g., panelists’ self-assessment of their skin). The best approach is to perform a seven-day mini regression,18, 19 applying test products daily on days one through four, and comparing untreated with treated skin. On days five through seven, the skin is allowed to regress without further treatment, which allows for the evaluation of the longer term effects of the treatment sample. In this scenario, measurements are taken initially and on days two, four and seven. A dryness scale is used to score subjects’ skin: 0 = no dryness; 1 = slight flaking; 2 = moderate flaking/scaling; 3 = marked scaling/slight fissuring; and 4 = severe scaling/fissuring.
Desquamation: Desquamatory methods utilize skin sampling discsa to collect cells from the superficial SC that are visually scored. The cells are then stained and their color evaluated with a colorimeter (C* value). This method can be used to measure the degree of flaking before and after use of a test skin treatment to provide a good determination of whether skin is alleviated.20, 21