In Vitro Moisturizing Test

Moisturizing is very important to maintain the beauty of the skin. Keeping the skin hydrated enhances the skin's elasticity, normalizes the skin's metabolism, and reduces the formation of wrinkles and pigmentation. Moisturizing is a basic and important function of cosmetics. Moisturization is the basic function of cosmetics. Moisturization testing can be performed using the capacitance method, which determines the moisture content of the skin stratum corneum at multiple points in time after a sample is applied to the skin. In addition, according to the mechanism of action of the product, in vitro and human evaluation methods can be selected to visually reflect the moisturizing efficacy of the product.

In Vitro Evaluation Methods

• Physicochemical method

A convenient means of evaluating the effects of cosmetics by testing their physical properties and the content of specific chemical components. For example, weighing method and physicochemical analysis method.

Weighing method - Under fixed temperature and humidity conditions, the interaction between the moisturizer and environmental water molecules is used to conduct experiments and calculate the moisture absorption rate and moisture retention rate to comprehensively measure the moisturizing effect of the moisturizer. When the moisture absorption rate is measured, the experimental sample is put into a dryer with high humidity, and then the dryer is put into a waterproof incubator with a set temperature of (20±0.1)℃, and the sample is taken out and weighed at intervals. From the difference in mass of the specimen before and after the experiment, the moisture absorption rate of the specimen is calculated.

In the determination of the moisture retention rate, a certain amount of moisture-containing samples are placed in a low-humidity desiccator equipped with dry silica gel, and are removed and weighed at intervals. From the difference in mass of the sample before and after the experiment, the moisture retention rate of the sample is calculated.

Physicochemical analysis method - Glycerol, polyethylene glycol and sodium hyaluronate, which are commonly used as moisturizers in cosmetics, were used as control samples to compare the moisture-absorbing and moisturizing properties of the yucca polysaccharides and the control samples in high and low humidity environments, respectively.

• Cell biology method

The cell biological method is a method of testing by establishing a cell model through human keratinocytes or fibroblasts cultured in vitro. The effect of moisturizers on skin cells can be investigated by observing the state of cultured cells before and after exposure to the test substance and by detecting the expression of proteins related to moisturization.

Human Evaluation Methods

• Skin moisture content and its distribution test

Skin moisture content test can directly reflect the moisturizing effect of the product. Currently, the main methods for testing skin moisture content are electrochemical and spectroscopic methods.

• Skin transdermal moisture loss test

Transdermal water loss (TEWL), also known as transdermal water loss, refers to the rate of water loss per unit of time from the dermis through the epidermis. The better the skin barrier function, the lower the TEWL value, so the change in TEWL value before and after the use of the product can be tested to evaluate the effect of cosmetic products or cosmetic ingredients on the improvement of the skin barrier function.