Zheng Muchuang,Lei Cuiting,Chen Chuwei

Guangdong yalijie Fine Chemical Co.,Ltd.,China

Abstract In order to explore the efficacy evaluation methods of skin repair cosmetics,30 qualified subjects were selected to evaluate the efficacy of a cosmetic claimed to have repair efficacy by three methods:TEWL test,lactic acid tingling test and visual photography.The results showed that the three test results were improved to some extent,and there were significant differences in percutaneous water loss rate and lactic acid tingling test results.Although there was no significant difference in erythema index results,its value also decreased to a certain extent.Therefore,transcutaneous water loss rate test,lactic acid tingling test and erythema index are effective methods to test the efficacy evaluation of cosmetics.

Key words cosmetic;repair;efficacy

In the Evaluation specification of Cosmetics Efficacy Declaration issued in 2021,the repair function could be claimed when the human efficacy evaluation test was correspondingly verified.However,there has been no standard unified testing system and test method in the country and the industry so far.According to the Evaluation specification,repair refers to the effect that helps to maintain the skin surface to ensure the normal state.Normal skin barrier should have certain stimulation tolerance,water locking ability,and immune function[1].It is usually measured by detecting skin barrier indexes such as lactic acid tingling test,skin transcutaneous water loss rate TEWL value and skin erythema index[1,2].The first indicator reflects the skin’s tolerance to the product,as lactic acid entering the skin will stimulate nerves to produce tingling when the skin barrier is damaged[1];the second indicator is the main parameter often used to evaluate the function of skin barrier through non-invasive objective detection[3-5];and the last index reflects the condition of facial capillaries and the degree of inflammation with the law that the lower the index,the better the effect of the product on repairing skin and improving skin erythema reaction[6-7].Combined with the above three indexes of subjects,this paper evaluates the efficacy of a cosmetic claiming to have skin repair efficacy,and discusses a simple and effective evaluation method suitable for skin repair cosmetics.The test results are reported as follows.

1 Experimental

1.1 Reagent and instruments

Repair essence,Guangdong Yajie Fine Chemical Co.,Ltd.L-lactic acid at 90% mass concentration,High purity grade,Macklin Company,China.Tewameter? TM300 probe,Courage + Kahazaka,Germany;VISIA-CR Skin Detection System,USA Canfield Technology,Inc.

1.2 Experimental method

1.2.1 Selection of the subjects

Thirty female subjects aged from 18 to 45 years old were selected for lactic acid prick test.

Exclusion criteria:Women currently pregnant or lactating;Those who used antihistamine within the last week or immunosuppressants within the last month;Application of any anti-inflammatory drugs at the tested site Within the last two months;Subjects having a clinically untreated inflammatory skin disease;Patients with insulin-dependent diabetes or asthma or other chronic respiratory diseases;Patients with immunodeficiency or autoimmune diseases;Those whose test results on the skin are affected due to scar,pigment,atrophy,port wine stain or other defects;Those highly sensitive;Subjects participating in relevant or other clinical trials and so on that may affect the test results within the last month.

1.2.2 Experimental procedures

This study adopted the method of an anterior and posterior control.After cleansing in the morning and evening,subjects took an appropriate amount of samples and applied it to the whole face n circles until it is absorbed and used,twice a day for 28 consecutive days.Clinical tests and evaluations were performed on days 0,14 and 28,respectively.

(1)Lactate tingling value score

The subjects cleaned the face and dried it with chip-free paper,and sat in a constant temperature(21±1) ℃ and constant humidity (50±5)% environment for 30 minutes.After applying the 50 uL of 10% lactic acid aqueous solution to their cheeks on either side of the nasolabial groove,the subjects evaluated the discomfort of itching,tingling and burning pain at the test site at 30 s,2.5 min and 5 min respectively.Score according to the 4-point method (0 for no sensation,1 for mild,2 for moderate and 3 for severe).

The cumulative tingling sensation scores of 30 s,2.5 min and 5 min was not less than 3 points,which is positive for lactic acid tingling[2].

(2)Skin transcutaneous water loss rate TEWL value

The Tewameter? TM300 probe was used to determine the TEWL value of the epidermal skin.

(3)Skin image uptake and analysis system

Using the VISIA-CR skin detection system,the facial tested area was selected to mainly determine the erythema index EI value of the detection region.

(4)Statistical method

Statistical analysis of the data was performed using the software.T-test or rank sum test was used to analyze the significance of the data before and after using the product,with P <0.05 meaning the difference is statistically significant and P <0.01 meaning the difference is extremely significant.

2 Results and analysis

A total of 33 subjects were recruited,and the final number of effective cases was 30 who were averagely (28.27±5.67) years.Fortunately,no adverse reactions occurred in subjects.

2.1 Lactate tingling score

Statistical analysis of lactate sting values at group in and out in this trial showed an extremely significant reduction (P<0.01),as shown in Table 1.It is seen that the subject's skin responsiveness to external stimulation,and the test product has a certain role in repairing the skin barrier.

In this test,the lactic acid tingling values at the time of entry and exit were statistically analyzed,which decreased significantly (P<0.01),as shown in Table 1.Therefore,it could be seen that the subjects’ skin was less responsive to external stimuli,which means that the test product has a certain role in repairing the skin barrier.

Table 1.Skin lactic acid tingling score

2.2 TEWL values

The test results of TEWL values were shown in Table 2,in which the sample value gradually decreased during the test.Compared with the base values,the TEWL values reduced significantly after both 14 and 28 days of using the product (P <0.05).Therefore,it can be seen that the repair product can significantly improve the skin transdermal water loss,which has the effect of protecting the skin barrier.

Table 2.Test results of skin TEWL value

2.3 Skin erythema index EI values

The test results of the skin erythema index EI values are shown in Table 3,in which the sample value gradually decreased during the test.Although there was no significant difference compared with that before use (P>0.05),the change rate decreased slightly.Therefore,it is seen that the sample has weak effect of improving the skin erythema reaction.

Table 3.Test results of skin erythema index EI value

3 Discussion

In this experiment,the repair effecay of repair cosmetics on sensitive skin with damaged barrier was observed,and the detection method of this effecay was studied by using three indexes:lactic acid tingling score,skin transcutaneous water loss rate TEWL value and the erythema index EI value.It was found that,after using the cosmetics,the lactic acid tingling score and the TEWL value gradually both decreased,both of which were statistically significant,respectively indicating that the skin’s responsiveness to external stimuli was reduced,the ability of the water locking and barrier function of the skin improved.

Although the skin erythema index EI value had no statistical significance before and after comparison,its gradually decreases reflected the degree of skin inflammation did not increase.

This test found that the lactate tingling score value decreased after using the test product compared with before use and was statistically significant,indicating that the skin had reduced responsiveness to external stimuli.Non-invasive instrument test results found that the skin TEWL value gradually decreased,and it was statistically significant,indicating that the product can significantly improve the skin water locking and barrier function.Although there was no significant comparison between the EI values,the EI value gradual decrease means that the degree of skin inflammation had not become severe.

The results of this study show that the indicators,including the lactic acid tingling score and skin transcutaneous water loss rate ,can reflect whether the skin’s ability to respond to external stimuli and the repair ability of skin barrier function are enhanced,thus supporting the detection result of skin repair effecacy of the sample.The erythema index reflects the regression degree of skin inflammation,and the analysis results do not fully meet the expectations,but also have a certain reference value.