Introduction: The aim of the study is to compare the biophysical parameters of the scalp of Alopecia group and Non-alopecia group with seasonal variations. Scalp repeatedly exfoliates and regenerates through a periodic desquamation. Keratinocytes and lipids such as ceramides and cholesterols form a ‘Brick and mortar’ structure, which acts as a barrier, protecting the body from trauma and pathogens and preventing water loss. In patients with androgenetic alopecia, follicles are miniaturized, causing erector muscle damage, sebaceous gland hyperplasia, and microinflammation, which means barrier function disruption. Therefore, we assumed that the pattern of changes in the scalp characteristics according to environmental factors would be different depending on presence-absence of alopecia. Thus we assessed and compared the biophysical parameters of scalp between Alopecia group and Non-alopecia group in summer (Average temperature: 26.6℃, average relative humidity: 79%) and winter (Average temperature: -0.7. ℃, average relative humidity: 60%), respectively.

Methods: Subjects were pre-screened according to Basic and Specific classification and divided into two groups; Alopecia group and Non-alopecia group. Biophysical parameters of the scalp (Scalp hydration, Scalp sebum content, Transepidermal water loss (TEWL) and Stratum corneum content) were measured with non-invasive methods. Results of the measurements were compared between summer and winter, and between groups. In winter, the samples of scalp keratinocytes were collected with stripping disc to analyze ceramides and dihydroceramides, which known as barrier-related lipids.

Results: Alopecia group showed statistically significant differences in all four biophysical parameters when compared between seasons. Comparing between groups, there were statistically significant differences in scalp hydration and TEWL in summer. Scalp hydration, scalp sebum content and TEWL in winter also showed differences, but there was no statistical significance. As a result of lipid analysis, the total amount of ceramides and dihydroceramides were higher in the Alopecia group, but there was no statistical significance.

Discussion: Based on the results, it was clear that there were differences between Alopecia group and Non-alopecia group in biophysical parameters. With seasonal variations, both Alopecia group and Non-alopecia group showed a big differences in the TEWL and stratum corneum contents, however, scalp hydration and scalp sebum content increased significantly only in Alopecia group, showing a more sensitive response to environmental factors compared to Non-alopecia group. We considered the disrupted barrier function to be the cause and analyzed the ceramides involved in the barrier function. Contrary to what was predicted based on former studies, lipid analysis showed no statistical significance between Alopecia group and Non-alopecia group in total amount of ceramides and dihydroceramides. Therefore, it is thought that further research is needed.

Conclusion: In this study, we hypothesized that the patterns of changes in the biophysical properties of scalp in Alopecia group and Non-alopecia group would be different depending on the external environmental factors, temperature and humidity. Comparing the scalp biophysical parameters according to the androgenetic alopecia with seasonal variations, there was a significant differences in scalp characteristics and in change patterns between the Alopecia group and Non-alopecia group, as expected. We thought that it would be related to the barrier function of the scalp, but there was limitations in result interpretation. In the next step, focusing on the scalp susceptibility to the temperature and humidy, we expect that research to develop on the correlation with the scalp barrier function and the mechanisms and hope that it will helpul as a fundamental data for the development of cosmetics, from seasonal scalp care products to products for scalp with hair loss.