Not being able to see a half-moon, or lunula, on the nails may be a sign of a vitamin deficiency, vitiligo, kidney failure, or another health condition. Some people only notice a lunula on their thumbs. Some causes can be serious, so it is best to contact a doctor.

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Nails grow from a pocket under the skin that doctors call the matrix. The matrix helps make new cells. These cells then come together and push out of the skin. The lunula, or lunulae in the plural, is the visible portion of the matrix, although it may sometimes be hard to see.

Skin color and other factors may make the lunulae more or less visible.

Because the lunula comprises the newest portion of the nail, it can provide clues about a person’s health. The absence of lunulae does not always indicate a serious health problem, but it is a good idea to discuss the issue with a doctor.

The following conditions may cause the lunulae to disappear or be less visible:

Malnourishment due to extreme diets, medical conditions that affect the body’s ability to absorb nutrients, and eating disorders can cause changes in the nails.

People with B-12 deficiency may notice that their lunulae disappear. They may also develop brownish-gray nails.

Blood tests can detect many vitamin and mineral deficiencies. A doctor can help a person determine what deficiencies they are most vulnerable to, depending on diet, lifestyle, health, and other factors.

Vitiligo is a chronic skin condition that causes the skin to lose color, usually in patches. This happens when the body attacks melanocytes, the skin cells that give the skin its color.

Some people with vitiligo may develop nail changes, including a loss of lunulae. A 2016 study of 100 people with vitiligo and 100 people without it found that nail changes were common with the disorder. However, 13 of those without vitiligo and 13 with vitiligo had no lunulae, suggesting that absence of lunulae may be equally frequent in both groups.

People with vitiligo may develop other disorders, such as thyroid disease, and they are more vulnerable to sunburns and other sun-related skin conditions. It is, therefore, important to seek medical care.

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People suffering from anemia may experience paleness that makes the lunulae invisible.

Anemia is a common blood disorder, affecting at least 3 million people in the United States.

It happens when the red blood cells that carry iron-rich hemoglobin do not work correctly or when the body does not produce enough red blood cells. This causes an oxygen deficiency that can result in paleness, including paleness that makes the lunulae invisible.

Iron deficiency is the most common cause of anemia, usually occurring when a person has either lost blood, such as following a hemorrhage or giving birth.

A deficiency can also happen when the body does not properly absorb iron, or a person does not consume enough iron-rich foods.

Other conditions can also cause anemia, including sickle cell anemia, exposure to toxic chemicals, and kidney failure.

People undergoing dialysis for kidney failure often do not have half-moons on their nails.

Doctors think this is because of anemia due to kidney failure. Kidney failure is not the only potential cause of anemia, or the most common. Therefore, it is important for people who think they might be anemic to see a doctor.

A person with kidney failure may also notice a brown band at the tip of the finger, at the point where the white tip connects to the nail bed.

The lunulae may turn red in people with certain types of heart and lung disease, including:

The nails may also change shape or texture, and a person may develop additional symptoms, such as shortness of breath, coughing, or chest pain.

Cirrhosis is a chronic condition that scars and damages the liver, affecting liver function. People with diabetes, those who drink excess alcohol, males, and people over 50 years of age are more vulnerable to cirrhosis.

People with cirrhosis may develop red lunulae. Their nails may also turn white, making it difficult to see the lunulae.

Some people develop deep-blue lunulae.

This nail change may be an early warning sign of argyria, which is a type of poisoning caused by excess silver exposure. People exposed to chemicals at work or to toxic chemical dust may develop argyria.

In most people, the lunulae of the toenails remain white, but a person’s hands, face, or eyes may turn blue.

Wilson disease is a genetic disorder that causes dangerous levels of copper to build up in the body.

This condition can cause a wide range of symptoms, including liver failure, tremors, anxiety, depression, clumsiness, and difficulty walking.

Some people with Wilson disease develop blue lunulae.

Some diseases cause the nails to thicken and turn yellow, obscuring the lunulae.

The nails may also curve, and the cuticle, which is the small piece of skin at the beginning of the nail, may change shape or disappear. The most common cause is pleural effusion, which happens when fluid accumulates in the pleura, or the thin tissues that line the lungs and chest.

Other conditions, such as poor circulation and swelling, may also cause the nails to be yellow and the lunulae to disappear.

People who have no lunulae but no other symptoms should not worry unduly. Sometimes the lunulae are simply not visible.

Nevertheless, it is a good idea to see a doctor to rule out possible medical conditions. This is because sometimes the disappearance of the lunulae is an early warning sign of dangerous conditions.

When a person has other symptoms, such as difficulty breathing, chest pain, a fever, or unusual swelling, the disappearance of the lunulae could signal a life-threatening health problem. In these cases, people should see a doctor immediately.

The nails reveal information about blood circulation, nutrition status, and how well various organs in the body are working. They act as an early alarm, warning of potential medical issues. In most cases, the absence or disappearance of the lunulae points only to a minor nutritional deficiency. Sometimes, however, the cause is more serious.

Seeking medical attention for any changes in the nails or skin can help a doctor detect serious medical conditions, as early as possible, enabling prompt treatment.