Nail health in Traditional Chinese Medicine depends on the harmony of the entire body, especially the liver
Traditional Chinese Medicine (TCM) has a long history of seeing connections between seemingly disconnected parts of the body. A good example of this is the connection seen between the nails and the internal organs. From its earliest texts, Chinese medicine has stated that the liver controls the sinews and its flourishing condition manifests on the nails.  What does this mean? What can be learned from it about nail health and its relationship to whole body health?
In TCM, each internal organ gives an insight into its state of health or disease through manifestations on the surface of the body. The nails, for example, give a small window into the health of a vital organ, the liver.
According to The Foundations of Chinese Medicine, if Liver-Blood is abundant, the nails will be moist and healthy; if Liver-Blood is deficient, the nails will lack nourishment and become rigid, dry, brittle and cracked. If there is a stasis of Liver-Blood, the nails will be dark or purple.  Additionally, another text states that when liver blood is abundant, nails are red, lustrous, and healthy. When liver blood is insufficient, the nails are pale and brittle. 
According to TCM theory, the liver stores the body’s blood and helps to regulate the amount of blood in the body according to one's physical activity level. Without this important function, during exercise, one would have less blood flowing to nourish muscles and tendons. At rest, this blood contributes to resting energy and the ability to be alert and clear-headed.
If for any reason someone becomes deficient in blood, either due to blood loss or poor blood production, the liver is not able to properly regulate blood flow. This disharmony can eventually lead to disease. Early indications of this disharmony can be seen in the liver’s manifestation onto the nails.
Interestingly, it is not just Chinese medicine that has noticed these connections between the liver and the nails. Nail abnormalities have frequently been associated with liver disease, particularly with liver cirrhosis, Hepatitis C, and Hepatitis B infections.  Specifically, brittle nails have been observed in patients with Hepatitis C. These patients had malnutrition, iron deficiency anemia, and decreased liver function tests which all lead to brittle nails. 
So what can be taught by Chinese medicine about health through examination of the nails? According to TCM, a deficiency of blood stored in the liver can lead to pale, ridged, and brittle nails. Many different conditions can lead to a state of liver-blood deficiency, most of which are not related to an actual state of anemia or low blood counts.
In Chinese medicine, a state of blood deficiency can be seen in subtle ways, such as the feeling of fatigue after a heavy menstrual period, or muscle cramps in athletes, after a particularly intense workout. These early symptoms can give an indication that the body is not properly nourished, even if blood tests are normal and there are not yet any clinical signs of blood loss or blood deficiency from a conventional medical perspective.
Some common causes of a deficiency of liver blood according to Chinese medicine are:
All of these, in one way or another, can lead to a disharmony in the liver’s ability to properly store and move blood throughout the body. When nails are breaking more easily, losing color, or forming ridges, traditional Chinese medicine considers the whole body’s health as part of the evaluation.
Nail brittleness can be an indication of a wide variety of conditions, including trauma, infection, systemic or dermatological disease, nutritional deficiencies and as a consequence of drug intake.