Many ingredients used in cosmetics evoke a comedogenic response. Rabbit ear model (REM) is a useful method that can replace human in examining materials and products in early developmental stage. However, a number of studies pointed out its disadvantage that it overreacts to comedogenic materials. The purpose of this study was to find the most appropriate region for evaluating comedogenicity in human skin.Methods:
Sixty-six female subjects (age 32.48 ± 10 years; range 20–52 years) with mild to moderate facial acne lesions were included in this study. The whole face, upper chest, and back of volunteers were photographed. Lesion (closed and open comedones) counting, instrumentation of sebum secretion level, and analysis of porphyrin number were performed. The entire study was performed under environmental conditions of specific relative temperature and humidity, controlled and maintained identically for each volunteer.Results:
In case of closed comedone, forehead showed a significant correlation with frontal cheek, lateral cheek, chin, and upper back. Meanwhile, significant correlations were observed between frontal cheek and chin as well as lateral cheek and chest. As for open comedone, forehead showed a significant correlation with chin site. A significant correlation was also observed between front cheek and lateral cheek as well as between upper chest and back. Analyzing the correlation between the occurrence of comedones and sebum in each region, a significant correlation between closed comedone and sebum was observed in frontal and lateral cheek. Analyzing the correlation between the occurrence of comedones and porphyrine in each region, a significant correlation between open comedone and porphyrin was observed in chin.Conclusion:
When evaluating the comedogenicity of cosmetics ingredients or products, this study recommends using both of the methods of testing on back and directly testing on face according to the characteristics of the materials. In case of mild potent ingredients or products in particular, verification through usability test that the directly test on face will help securing reliability.