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"Dampness" is one of the Six Climatic Factors—"wind, cold, heat, dampness, dryness, and fire." In the natural world, there are the Six Climatic Factors—external Six Climatic Factors—which pertain to environmental and climatic configurations. The human body corresponds to the natural world, being a holographic element within it, forming a microcosm. Therefore, it also has the Six Climatic Factors—internal Six Climatic Factors. In Traditional Chinese Medicine (TCM), the spleen governs the "internal dampness" within the human body. Thus, Huangdi Neijing-Zhizhenyao Da Lun states, "All dampness syndromes with swelling and fullness are ascribed to the spleen," attributing dampness and edema-related conditions to spleen disorders.

"Dampness" in Chinese has two written forms, "溼" and "濕." Breaking down the characters: "氵" indicates that dampness is related to "water," "土" represents its connection to "earth," "─" symbolizes "heaven," "ㄠㄠ" signifies the evaporation between heaven and earth, "日" represents the sun, and "灬" stands for "fire and heat." In summary, "dampness" refers to the moisture in the soil and the vapor that rises into the air due to taiyang or geothermal heat. The natural world requires an appropriate level of "dampness" for all things to grow properly; excessive or deficient dampness is detrimental to life, and the soil contains the primary source of this moisture.

Imagine food scraps or the remains of plants and animals being discarded onto the soil, naturally decomposing into various small molecules that become nutrients for other organisms. This process requires an appropriate balance of air, taiyang light, water, and geothermal heat—collectively, this is the "dampness" of the land. In the human body, after food is ingested into the digestive system, it is automatically broken down into fine molecules to nourish the body's cells. This process also requires water, digestive fluids, and heat—collectively, this is the "dampness" within the digestive tract, which serves as the "soil" of the human body.

Therefore, "dampness" is not inherently bad. The earth requires an appropriate level of dampness for all things to grow. Similarly, the "earth" within the human body—the digestive tract—also needs the right amount of "dampness" for digestive functions to operate normally. The entire body also requires an appropriate level of dampness to remain moisturized and for various functions to operate properly. Problems arise only when there is too much or too little dampness.

When digestive function is impaired, the body's dampness becomes imbalanced. In TCM, this is referred to as "spleen deficiency failing to regulate water dampness" or "earth failing to control water." Excessive water dampness can lead to abnormal bowel movements, loose stools, diarrhea, and a tendency for the body to accumulate dampness, feeling heavy. Severe water dampness can result in noticeable edema.

One-third of the body's water is expelled through evaporation from the mouth, nose, and skin, which is an essential part of the body's fluid circulation. If the humidity in the air is too high, the evaporation of moisture from the body surface decreases, leading to more water retention on the skin or even inside the body. As a result, external dampness can cause internal dampness, making the body feel heavy. When dampness affects the head, it may feel as if it is wrapped tightly; when it affects the limbs, it may cause heaviness and weakness. Living in a humid environment for a long time can more easily lead to chronic internal dampness.

Here lies a question: The spleen and earth regulate dampness, and it is understandable that "dampness" exists within the digestive tract. But how do the spleen and stomach extend their influence beyond the digestive tract to regulate "dampness" in the limbs?

Within the human body, clear fluids and red blood flow in separate spaces. Blood flows within blood vessels, while fluids flow within lymphatic vessels and interstitial spaces. Fluids and blood are two sides of the same coin. Fluids seep from capillaries into interstitial spaces, with 90% returning to capillaries and 10% flowing into lymphatic vessels, which eventually return to the large veins. Blood and fluids circulate in this manner, endlessly. For reference, see triple energizer.

If more fluid than usual seeps out of blood vessels, the interstitial fluid increases, leading to a sense of heaviness in the limbs. Excessive fluid seepage from capillaries can cause edema. When does this happen? It occurs when the osmotic pressure within blood vessels is lower than usual. Osmotic pressure is determined by the concentration of solutes in the fluid. For example, the saltier the water, the higher the osmotic pressure, and the greater its ability to absorb water.

The difference in osmotic pressure between blood vessels and interstitial spaces determines the direction of fluid flow, primarily influenced by the composition of both.

   Blood - Blood Cells - Macromolecular Proteins = Interstitial Fluid = Lymph

Blood contains more blood cells and large molecular proteins than other body fluids, while other components are the same in both. Therefore, when the density of blood cells (mainly red blood cells) or large molecular proteins in blood vessels decreases, the osmotic pressure of the blood vessels will be lower than normal, and vice versa.

At this point, the influence of the spleen and stomach on the osmotic pressure of blood vessels becomes evident. This is because the production of blood cells or proteins requires nutrients, and only a healthy spleen and stomach can absorb sufficient nutrients to supply the production of blood cells and proteins. When the function of the spleen and stomach is weak, blood cells↓, large molecular proteins↓, and the osmotic pressure of the blood↓, causing more water to move into the interstitial spaces, leading to the phenomenon of "heavy dampness," and in severe cases, edema.

Here, the author proposes a key point: almost all proteins in the blood are synthesized by the liver. Even if the gastrointestinal function is sound, if the liver function declines and the synthesis of proteins is insufficient, it can also lead to heavy dampness or edema. Therefore, the liver also plays a role in controlling dampness, but TCM does not consider the liver to directly control dampness. Thus, the "spleen earth balancing dampness" actually encompasses some functions of the anatomical liver.

In addition, "Spleen Governing Transportation and Transformation" does not mean that the digestive system has the ability to actively transport body fluids throughout the body. The spleen system belongs to "earth" in the Five Phases. In nature, earth can contain dampness, but the earth does not have the ability to actively transport dampness. The dampness in the world is driven and circulated by the light and heat of taiyang or geothermal heat. Moreover, the only thing that can actively transport water is plants, and the dampness in the soil is mainly held by plants. The liver, which belongs to "wood" in the Five Phases, is like the "plants" growing on the spleen, and its ability to regulate dampness is self-evident.

Of course, not all edema is due to spleen dampness. There are many causes of edema, and careful consideration is required, such as:

• Kidney disease: Mild cases start with edema in the eyelids and face, and in severe cases, it develops into whole-body edema.
• Liver disease: Often presents with abdominal swelling (ascites) and lower limb edema.
• Heart failure: Difficulty in blood return, often starting with lower limb edema; renal blood flow also decreases, leading to reduced urine output and worsening edema.
• Poor gastrointestinal function: Poor nutrient absorption, even if the liver is healthy, it cannot synthesize enough plasma proteins, leading to limb edema.
• Long-term malnutrition: Insufficient protein intake, resulting in the same outcome as poor gastrointestinal function.
• Drug side effects: Such as long-term use of NSAIDs, vasodilators, or calcium channel blockers.