## 3 Results and Discussion
### Discussion
However, the study did not compare age or gender, was restricted to a single depth, and did not discuss the relative variation across depths. In contrast, our investigation focused on the dynamic changes within the skin layer by using the dynamics of OCT images for different depths and different genders. Our main findings are as follows:  
In terms of depth comparison, only at shallow depths close to approximately 100 \(\upmu\)m, possibly in the papillary dermis layer in the epidermis-dermis border region, a significant difference was observed in the average contrast between the before heating and after rest conditions. Considering the depth and the organization of the vasculature within the skin, this seems to be reasonable as the microvasculature occurs in the upper layer of the dermis, which is almost at the papillary dermis layer and epidermis-dermis border. From the existing data available of the measurements of epidermal thickness [1; 17], the ROI1 selected for our study was almost at the papillary dermis layer, possibly on the border. This could also be seen from the bOCT images where we observed a higher density of the red region, suggesting the presence of microvasculature. With respect to age groups irrespective of gender, for both age groups, there were significant differences depending on the condition. For the younger group, there was only a statistically significant difference in average contrast soon after heating with respect to before heating. On the other hand, for the older group, there was a significant difference of the contrast between before heating and soon after, as well as between before heating and after 5 min of rest. This suggests that age plays a larger role in the control of vascular dynamics, as reported in other studies [1; 2; 17]. With respect to gender, there was a significant difference between males and females for both soon after heating and after 5 min of rest, with no significant difference for before heating. These gender differences could be the result of differences in the skin thickness as well as the vascular density. There are reports that hormonal differences play a larger role in the vascular dynamics in the control of skin under heat stress, though the mechanism behind the reason for gender differences is not clearly understood yet [8]. Ours is the first study to make use of temporal variation and investigate the changes in the variability of the OCT signal. We also conducted a comparison of the effects of gender and depth. Specifically, we found the results to vary based on depth, age, and gender. Although our study revealed significant differences with respect to gender, we still do not have a clear explanation for the gender-related changes. In the case of females, both estrogen and progesterone appear to influence skin blood flow control in both young and postmenopausal women. While estrogen has the role of promoting cutaneous vasodilation and, thus, heat dissipation, the effect of progesterone is less clear, although it possibly inhibits cutaneous vasodilation [15]. Although our results with respect to gender and age group studies are limited by sample number, we believe our current bOCT system could possibly be sensitive enough to detect changes. In this analysis, we restricted our study to shallow depths of within 200 \(\upmu\)m, where we found that the speckle contrast showed statistically significant differences. In the future, the application of our technique could pave the way for conducting studies in deeper regions and it could have clinical implications for diabetic mellitus [7] and heart-related diseases [6], for example. In total, our results demonstrate that bOCT could be successfully implemented for the study of the environmental effects on skin tissue, and we believe that this has potential implications in therapeutic treatments such as warm water immersion [16].