Background: Different wavelengths of ultraviolet (UV) light cause skin damage through different mechanisms. Minimal erythema dose (MED) is usually used to clinically evaluate skin sensitivity to ultraviolet radiation by inducing skin erythema using ultraviolet B (UVB) or ultraviolet A (UVA) + UVB.Aims: In this study, we detected changes in the blood flow at the MED erythema caused by UVB and UVA + UVB radiation through optical coherence tomography (OCT) to explain the role of different bands of ultraviolet rays in erythema induction.Methods: Two MED irradiation areas on the subjects' back were irradiated with UVB alone or UVA + UVB (UVA: UVB = 8:1). The absolute energy of UVB remained the same in UVB and UVA+UVB. At 24 h after the irradiation, the changes in the blood flow in the MED area were detected using OCT.Results: Compared with the blank control, the maximum blood flow depth, blood flow peak, and total blood flow of UVB-MED and UVA+UVB-MED were significantly increased. Notably, the maximum blood flow depth and blood flow peak of UVB-MED were higher than UVA+UVB-MED. There was no significant difference in total blood perfusion between UVA+UVB-MED and UVB-MED. Under the same UVB energy, the skin erythema caused by UVA + UVB was weaker than UVB alone.Conclusions: The analysis of local blood flow by OCT showed that the peak and maximum depth of local blood flow caused by UVB alone were significantly higher than UVA + UVB.

Background: Following the sufficient studies of the effects of skin barrier impairment and heightened neural reaction on sensitive skin (SS), many scholars have paid great attention to the roles of superficial microvasculature in SS.Methods: By questionnaire survey, lactic acid sting test, and capsaicin test, eligible subjects were classified as normal skin, only lactic acid sting test positive (LASTP), only capsaicin test positive (CATP), and both positive (both LASTP and CATP). D‐OCT was used to photograph images for evaluating the cutaneous vessels features each group.Results: Totally 137 subjects completed the study. Compared with LASTN group, the vascular vessels were closer to epidermis in LASTP group. Mesh and branching vessels were more popular in SS than normal skin. High blood vessel density was more prevalent in SS, while low density frequently presented in normal skin. The vascular depth had a closely negative correlation with face flushing and SSS, and vascular shapes had a good positive correlation with face flushing and SSB.Conclusions: Our study indicates that there is a significant difference in vascular depth, shape, and density between SS and normal skin which is valuable to explore SS pathologic mechanism and to further investigate cutaneous microvasculature functions in SS.

Background: Minimal erythema dose (MED) has substantial inter‐ and intraindividual variations, reflecting the influence of very diverse factors. However, related studies showed little consistency probably because of their limited sample size.Objective: To identify the factors associated with MED variations in a large‐scale population study.Methods: The MED test was performed by following the international standard procedure on 22 146 subjects. The results were analysed in adjusted multivariable linear and logistic regression models.Results: This large‐scale study revealed that lower MED was consistently associated with lighter skin [β‐coefficient = −0.33, 95% confidence interval (CI) −0.36 to 0.30, P = 6.41 × 10⁻⁸⁴]. Females had significantly higher MED than male (β = 0.91, 0.32–1.50, P = 2.93 × 10⁻³). Stratified analyses showed that MED was not associated with age [female: odds ratio (OR) = 0.99, 0.98–1.01; male: OR = 0.99, 0.97–1.00]. MED was lower in summer than in other seasons (spring: OR = 1.08, 1.06–1.11; autumn: OR = 1.11, 1.08–1.13; winter: OR = 1.20, 1.18–1.22). Furthermore, MED was associated with air temperature (β = −0.36, −0.49 to 0.23, P = 4.81 × 10⁻⁸) and air pressure (β = −0.64, −0.82 to 0.46, P = 8.01 × 10⁻¹²) in summer only while not in other seasons.Conclusions: This study provides unprecedented evidence that MED is associated with skin colour, sex, season and meteorological factors, but not with age.

Background: Evidence suggests that sebum content is important in skin disorders such as acne. However, sebum levels change depending on the external environment, and quantifying skin sebum levels is challenging. Here, we propose an optimal method for quantifying the facial sebum level.Materials and methods: Four hundred and sixty participants (160 males and 300 females) aged 20–40 were enrolled in this study. A Sebumeter SM 810 was used to measure the sebum level at five facial locations: the forehead, the chin, the left cheek, the right cheek, and the nose. The participants were divided into two groups; one group underwent a one‐time measurement (n = 390, male: female = 120: 270), and the other underwent three consecutive measurements (n = 70, male: female = 40: 30). The casual sebum level (CSL) was measured in all patients after a 30‐min acclimatization; subsequently, the sebum removal process was conducted, followed by a resting period of 1 h to determine the sebum excretion rate (SER). Spearman's correlation analysis and the Wilcoxon signed‐rank test were used to compare the sebum level consistency and differences between the groups.Results: Although three consecutive measurements better reflected the sebum content, the one‐time measurement also represented the relative sebum level. One hour after sebum removal, the sebum level recovered to 70%–90%; thus, this method was applicable for use in SER quantification. Of the five testing points, the sebum content was highest in the nose and lowest in the cheeks (both left and right). In addition, the cheeks were the most stable sites in terms of testing points, testing times, and CSL/SER values. A one‐time measurement of the CSL could represent the SER 1 h after the sebum removal. In our cohort, the sebum level of males with oily skin was decreased at age 32–35, and that of males with non‐oily skin increased at 28–35. The opposite trend was observed in female participants.Conclusion: Sebum measurement methods were assessed, including testing times, indices (interval of time) and sites in a conditioned external environment. A one‐time measurement of the CSL 1 h after sebum removal was sufficient to determine the sebum level and SER, and the cheeks are recommended as the testing site. Sex and skin type differences were observed in sebum level changes with age.