The biggest benefits of skin brushing come through the way that it stimulates and assists the functioning of the lymphatic system, so this post is dedicated to explaining how that system works.
We generally know more about the blood circulatory system than the lymphatic system, so let’s start there. The two systems work closely together, so understanding them both is helpful.
The blood circulation
The blood circulates in a closed system through the arteries and veins of the body and back to the heart and lungs to be re-oxygenated. Pumped by the heart, our blood moves through its vessels under significant pressure. This hydrostatic pressure drives some of the blood plasma out of the arterial capillaries (those travelling away from the heart). The plasma leaving the capillaries carries oxygen from the lungs, hormones from the endocrine glands, and nutrients collected from the digestive system. It joins the interstitial fluid, which bathes the cells of the body’s tissues, feeding them and collecting their carbon dioxide and wastes. The interstitial fluid contains more water than blood does, and water always tries to reach an equilibrium. This creates osmotic pressure that drives some fluid, containing CO2 and wastes from the cells, back into the venous capillaries (those taking blood back to the heart), where hydrostatic pressure is slightly lower. Gases, nutrients and wastes are exchanged via this diffusion of fluids, and the blood itself never leaves the vessels.
Lymph and the blood system
Most interstitial fluid re-enters the blood system this way. However, because the hydrostatic pressure in the blood vessels is generally greater than the osmotic pressure outside them, more fluid leaves the blood than re-enters it. Without being drained away, this extra fluid would build up, resulting in oedema (swelling) and eventually death. Throughout the tissues, draining away this excess of fluid, are the lymph vessels. These vessels begin blind, meaning that unlike blood vessels they do not form a closed circuit but make up a one-way system carrying fluid away from all over the tissues back to the blood system. About 10% of interstitial fluid enters the lymph vessels, where it becomes known as lymph. The lymph vessels eventually converge to drain the lymph back into the blood supply just before it reaches the heart. Lymph from most of the body is drained via the thoracic duct (which runs up the centre of the torso) into the left subclavian vein. Lymph from the upper right quadrant of the body (the right arm and the right side of the head and chest) drains via the right lymphatic duct into the right subclavian vein. The subclavian veins are situated below the neck just above the heart.
Lymph and the immune system
Because the lymph began as interstitial fluid bathing the cells of all our tissues, it carries samples of any antigens that are present anywhere in the body. (Antigens are any foreign proteins, such as bacteria, viruses or cancer cells.) On its way through the lymphatic system, the lymph passes through various lymph nodes and other areas of lymphoid tissue. The main purpose of the lymphoid tissue is to provide immune functions that help our bodies fight infections and prevent the growth and spread of tumors. Lymphoid tissue is made up of connective tissue with various types of white blood cells, especially lymphocytes, enmeshed in it. Lymphoid tissue can occur either in specially organised organs and nodes, or in areas of lymphoid follicles within other tissues, notably in the skin, where it is known as skin-associated lymphoid tissue (SALT).
As lymph percolates through our various lymph nodes and areas of lymphoid tissue, foreign particles are filtered out and identified. When lymphocytes encounter an antigen in the lymph, they immediately respond by multiplying and adapting into factories, creating antibodies to trap and destroy the foreign material, and begin releasing these into the lymph system, and in turn into the blood system. These specially adapted lymphocytes and their antibodies will thus begin to circulate through the entire body, eliminating the foreign substances as they encounter them. A well-functioning lymphatic system will respond quickly to any infection and continually reduce toxins in the body to non-carcinogenic levels.
The flow of lymph
In order to perform its important functions, lymph needs to keep flowing. A slow-moving, sluggish lymph system means the body has a slower immune response, and toxins, pathogens, cancer cells etc. all have more chance to accumulate in the tissues, where they can do harm and proliferate undetected. When lymph nodes are overloaded with foreign matter and lymph is flowing slowly, they can even become clogged and infected themselves, hampering the immune system still further. Yet unlike the blood circulation, the lymphatic system lacks a pump to keep lymph moving through the body.
Lymph moves in one direction only, ultimately towards the subclavian veins, where it pours into the blood supply just above the heart. To move lymph, the lymph vessels are equipped with tiny muscles that contract in sequence, pushing lymph along in a peristaltic motion, with valves at intervals to prevent back-flow. This motion is relatively weak however, and lymph is helped around the body largely by the action of our muscles contracting during exercise and by our lungs as we breathe. Both of these actions push against the lymph vessels and keep the lymph flowing. This is one of the main reasons why regular exercise and practicing deep breathing are beneficial to the immune system.
The skin and the lymphatic system
Another way to stimulate the lymphatic system directly by assisting the flow of lymph, as well as to achieve several other health benefits, is skin brushing. Although distributed throughout the body, most lymph vessels occur just below the surface of the skin, in the dermis. The skin is the largest organ of the body and one of its its primary organs of elimination. It is also often the site at which the body first comes into contact with foreign substances. So the lymphoid tissue in the skin is especially important. Skin brushing helps to keep the pores unblocked and the lymph flowing swiftly through the skin. This means that more of the tasks of identifying and eliminating toxins and wastes can be achieved here, putting less strain on the rest of the lymphatic system and the body’s other organs of elimination (liver, kidneys and colon). Encouraging the flow of lymph in the dermis also has an effect on the entire system, helping lymph flow better throughout the body.
Another important job of the lymphatic system is to transport fats and fat soluble vitamins from the digestive system to other tissues to be metabolised or absorbed. During digestion, most nutrients absorbed by the small intestine are passed via the blood to the liver to be processed. Most fat molecules are too large to diffuse into the blood system however. Instead they enter special lymph vessels surrounding the small intestine called lacteals. (An exception is medium-chain triglycerides, such as those found in coconut oil, which do diffuse directly to the blood. This is one reason coconut oil is so easy for the body to process and use.) The fatty acids mix with lymph to form a milky substance called chyle. Chyle then flows into the blood system via the thoracic duct.
The lymphatic system in summary
- Fluid from blood leave the vessels to form interstitial fluid (the fluid in the tissues).
- Some of this fluid is taken up by lymph vessles, becoming lymph.
- Lymph is moved through the lymphatic system via lymph vessels.
- It percolates through various lymph nodes and areas of lymphoid tissue.
- The lymphoid tissue constantly filters out and identifies foreign particles (antigens).
- Antigens are presented to the lymphocytes, which in turn create the tools to fight them (antibodies).
- Other vessels (lymphatics) transport lymph back to the blood via the thoracic duct.
- The lymph and blood circulation deliver antibodies to whatever site in the body they are needed so that the antigens can be destroyed.
- Specialised lymph vessels carry fats from the digestive system to the blood supply.
I hope that this description of the lymphatic system helps explain why dry skin brushing, and any practice that stimulates the lymphatic system to keep moving and functioning well, is such a valuable investment in our health.