According to the Classification Rules and Classification Catalogue of Cosmetics, moisturization is defined as the category of efficacy that replenishes or enhances the content of moisture, oil, and other ingredients in the application site, and helps to maintain the moisture content of the application site or reduce moisture loss.
Currently, the widely recognized moisturizing human efficacy evaluation method in China is Guideline for Evaluation of Cosmetics Moisturization Efficacy issued by the Ministry of Industry and Information Technology in 2011, and EnterCo's self-built Innoderm cosmetic efficacy testing laboratory is also based on this standard to carry out cosmetic moisturizing human efficacy evaluation tests.
Moisture content of skin stratum corneum by capacitance method
The capacitance method is used to determine the moisture content of human skin stratum corneum based on the significant difference in the dielectric constants of water and other substances. According to the different moisture content of skin stratum corneum, the measured capacitance value of the skin is different and its parameters can represent the moisture content of the skin.
Select 24-30 qualified subjects, and randomly select product application areas and blank control areas from the left and right arm areas of the subjects, ensuring that all product application and blank areas are statistically balanced.
After the application of the test sample, measurements of the product area and the control area are performed, with each area measured at least three times in parallel. The initial value of each test area (before sample application) is measured first, and then the skin moisture content of the tested area and the control area is measured after a set time. The setting time should be greater than 1h, and multiple measurement points can be set for 2h, 3h, etc. depending on the product evaluation needs, usually not exceeding 24h.
Data collection and analysis:
Descriptive statistics are conducted on the measured values of each testing area, including quantity, mean, standard deviation, minimum, median, and maximum values.
Calculate the difference between the initial values of a testing area and the measured values at other time points, and then use this difference to statistically analyze the differences between the product area and the blank control area at different time points.
If the test data is a normal distribution, the t-test method should be used for statistical analysis; If the test data is a non-normal distribution, the rank sum test method should be used for statistical analysis.
A two-tailed test is used for all statistical methods, with a testing level of α=0.05.
Positive result: There is a significant difference in the moisture content of the stratum corneum before and after the use of the product, indicating that the test sample has a moisturizing effect.
Negative result: There is no significant difference in the moisture content of the stratum corneum before and after the use of the product, indicating that the test sample does not have a moisturizing effect.
In addition to the instrumental data, the Innoderm cosmetic efficacy lab also combines the results of the subjects' self-assessments to determine whether a product has a moisturizing effect.
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