The blood is kept flowing continuously through a closed system of blood vessels. Every part of our body has a dense network of microscopic blood capillaries. In fact, every tissue cell is within 0.02 mm of a blood capillary. It is at the capillaries that exchange between tissue cells and blood takes place. (Source)

In other words, the health of the skin depends on the cells IN the skin. Those cells, like any other cells in the body, depend on the existence and proper function of CAPILLARIES to get the nourishment that the blood can provide.

If the person does not eat properly, the nourishment will not be in the blood.

Even if the person eats properly, and the nourishment is IN the blood, if that blood does not reach the cells -- any cells -- the cells will be in poor health.

Since ALL cells are nourished from the blood in capillaries, you would expect to find more and better explanations of the system of capillaries in our bodies.

You do not find that information without considerable digging.

First, you will find widely different data on the length of all the capillaries in the body. Here is a usable source:

The microcirculation is the business end of the vascular system and with its 60,000 miles of capillaries in the human body is responsible for the transport of nutrients and metabolites to the body's many tissues. Perfusion of the microvascular network (comprised of the capillaries and associated small vessels smaller than the thickness of a human hair) is strongly dependent upon the mechanical properties of blood cells and the vessel wall. (Source)

Here is a "popularized source" which includes a simple experiment designed for children -- to teach them the nature of capillaries.

Our bodies contain thousands of miles of blood vessels. Enough to circle the earth 2 1/2 times if laid out end-to end! Arteries and veins are the main throughway for blood to carry cells. But in between veins and arteries are these tiny vessels called capillaries. Capillaries only can allow red blood cells to pass in a single-file line! This experiment helps to illustrate how blood cells are able to fit through the tiny capillaries. (Source)

You have probably not heard that breathing more deeply, as while doing exercise, can increase the amount of capillary length as well as blood supply to the skin (as well as the whole body).

On a purely physiological level, if you learn how to breathe deeper and more powerfully --with exercise, for example--you actually grow more capillary space in your body.

There are about 60,000 miles of capillaries in your body. But if you're a regular exerciser, you have a lot more than that. You may have another ten or twenty thousand miles of capillary space in your body, so you've literally got more space for feeling in your body. (Source)

I first learned about capillaries when I was doing vigorous exercise and using a heart rate monitor to measure my heart rate with different types of exercise.

I was astounded to learn, from this personal observation, that I could do the exact same (treadmill) exercise with "proper" breathing or with the same 'ole breathing I had been using for 70 years. I found that I could change my heart rate by as much as 20 beats per minute simply by changing the way I breathed.

There is so much to this -- because I also then took up Kung Fu. I actually spent 60 days, 7 days per week, sitting in a sauna for some hours where I practiced the proper breathing. It was not at all natural for me to do -- it was very common for me to be mentally distracted (just think about lunch, etc) and my breathing would revert to the old type.

Now, a year later, with Kung Fu classes twice weekly, I have learned the great importance of proper breathing -- and thank my Kung Fu Grand Master for deeper and better understanding of this amazing data.

There is a link HERE to a very wonderful article on "breathing" and I urge you to read it all -- carefully. You will see that just proper breathing can improve the health and beauty of your skin -- and your life!

Yes!

In normal respiration the air is taken in through the nostrils without any special effort, sound or exaggerated movement of the nose or chest. In short, it is done unconsciously. We are not even aware of air traveling through our nostrils, down the nasal and oral parts of the pharynx, of its reaching the larynx and then the trachea and the lungs. In general, most of us are unaware of how the breathing process works.

. . . .

There are voluntary control of breathing. For example, you can deliberately take a deeper breath or stop breathing momentarily. Such direct control may be supplemented by indirect intentional control, as when we dance or kiss or drink or smoke or sing. We may deliberately run for such a distance that we get our "second wind," after which we breathe more easily even though exercising strenuously.

Part of the significance of distinguishing between voluntary and involuntary control of breathing is that yogic exercises aim first at changing unhealthy involuntary patterns voluntarily and then at an establishment of more healthy patterns. Whereas nervous tension produces some inhibiting influence upon deep, regular breathing patterns, deliberate effort to counteract these influences in such a way that our more completely spontaneous and uninhibited rhythmic patterns become restored as needed. (Source)