Confirming the links between skin condition and regulation of capillary blood flow:
An image analysis technology to visualize capillaries in facial skin

Kao has been researching the relationship between skin condition and physical functions such as the blood circulation from a dermatological perspective as the skin is part of the whole body system. In 2015 this research led to the discovery that people with higher capacity to regulate blood flow in response to environmental changes tended to be people with less skin dryness. Vascular reactivity is reported to be linked to mental stress.^{*1 ,*2}
Capillaries are fine blood vessels branching away from the veins and arteries throughout the body. They perform the most essential function in the circulatory system by exchanging materials between the blood and tissue cells, that is, supplying oxygen and nutrients to the tissue and removing waste matter from the tissue. The mechanism by which capillaries regulate blood flow differs from the veins and arteries. Specifically, the capillary blood flow is regulated by the oxygen concentration of the tissue and metabolic activity.
So far it has been impossible to precisely visualize and measure the extremely fine capillaries by discriminating them from the surrounding tissue. Much has yet to be learned about the relationship between the workings of the capillaries and the functions and metabolism of the skin and skin beauty.

In 2017 Kao researchers used a microscope to examine the capillaries in the skin of 98 Japanese women in their twenties to their sixties. The goal was to examine how the skin condition correlates with the blood flow regulatory function of the capillaries^*3 or the area, length, and density of the capillaries in a resting state. The results revealed that the blood flow regulatory functions correlate with more parameters of skin conditions than the regular capillary condition.

An analysis based on differences in age further revealed that women in their twenties and thirties with higher blood flow regulatory function tended to have better skin texture pattern. On the other hand, women in their fifties and sixties with higher blood flow regulatory function have smaller cell sizes in the stratum corneum^*4 . This suggests epidermal cells were activated (Fig. 2).

In order to examine the relationship between capillary blood vessels and skin condition in greater detail, Kao researchers developed an imaging technology to visually extract capillaries with high precision under a microscope.
The presence of melanin and hair in and on facial skin makes it difficult to measure capillaries by conventional imaging techniques. To solve this problem, images of the capillaries inside the skin can be divided into separate independent components of hemoglobin, melanin, and shade. Filter processing is then applied to the hemoglobin images to visually discriminate the capillaries based on their tubular structure. Masking is then performed using images generated from the shade component to attenuate the noise innate to hair. With this method, Kao researchers have constructed an algorithm for precisely discriminating the capillaries in microscopic images (Fig. 1).
To confirm the precision of this process, the algorithm was compared with conventional measurement by trained experts annotating the microscopic images of the capillaries manually. In this comparison, 96.6% of all the extracted images were in alignment with the annotated area. Capillaries in the skin were visually extracted with high precision in a matter of seconds.

Kao researchers found a connection between the blood flow regulatory function of the capillaries and skin conditions. This finding, coupled with earlier research, strongly suggests that blood flow regulatory function is linked to skin beauty. The development of a new evaluation method combining this visual discrimination algorithm and quantitative measurement of the capillaries from microscopic images of the skin will make it possible to assess the state and functions of capillaries and more fully investigate the links with facial skin.
In the future Kao researchers plan to study changes in the condition of the blood vessels brought about by aging and the environment and to analyze the effects on various phenomena such as skin metabolism, dark spots, and fine lines.