## 4 Discussion
In this study, pulsed-type bipolar RF microneedling devices decreased NET (number of lesions exceeding the erythema threshold) and pixel % (summation of the area exceeding the erythema threshold) when comparing each visit to the last visit. Previous studies have only performed subjective evaluations of erythema or only evaluated local erythema indexes [8]. However, in this study, the exact severity of erythema was evaluated after correcting the brightness, depth, and color of the entire photo of a patient's face using a skin analysis system. After that, we accurately obtained erythema lesions using CIELAB. Observed clinical improvement in the present study was consistent with previous studies [8; 9; 10]. We set two variables: the number of lesions exceeding the erythema threshold (NET) and the summation of the area exceeding the erythema threshold (pixel %). In rosacea, the erythema of the entire face is important, but post-inflammatory erythema related to acne usually appears sparsely. Therefore, analyzing lesions above a certain threshold of redness was necessary. Using CIELAB, the number of red lesions exceeding a certain threshold and the sum of the total area were set as disease severity. This study showed that a bipolar pulsed RF treatment could significantly reduce the number and area of acne and erythematous lesions. The mean number of NET (the number of lesions exceeding the erythema threshold) at three sites (the forehead, left malar, and right malar) was significantly decreased after the treatments. It indicates that the number of acne and acne scars has decreased. Additionally, Pixel % (the summation of the area exceeding the erythema threshold) was significantly decreased in two sites (left malar and right malar). It means the area affected by acne has improved. Although the area index on the forehead did not significantly improve, it might be due to obstacles such as hair while taking photos. In this paper, to evaluate each aspect in more detail, our analysis compared adjacent visits. Significant differences were confirmed between visits one and two at three parts (NET of the forehead, pixel % of the forehead, and pixel % of the right malar), and between visits two and three at one part (right malar). According to this result, treatment response is significant in the early phase. This clinical improvement is consistent with the previous study [8]. Adverse effects such as pinpoint bleeding and pain were noted. However, they were transient and not severe enough to stop treatment. Other treatment-related adverse effects, such as hyperpigmentation, bruises, purpura, or infections, were not observed. Our study has several limitations. First, it was a single-centered retrospective design. There may be selection bias because of the single-centered design and the small number of patients included. Second, since this study does not include a control group, the analysis was conducted only in time-variables without control in a repeated ANOVA (analysis of variance). Additionally, patients taking oral medications such as doxycycline and minocycline were included in this study. A multi-centered study with more patients and more control, including oral medications, might be needed.