What’s the half-moon shape on my fingernails?

The half-moon shape at the base of your fingernail is known as a lunula. Lunulae cover the bottom of your nail, just above your cuticle.

Lunulae are part of your nail matrix. The matrix refers to the tissue just beneath your nail. It contains nerves, lymph, and blood vessels. It also produces the cells that become the hardened nail plate, which is what you see.

Although everyone has a nail matrix, not everyone will see or have a lunula on each nail. Those who do have a lunula may notice that they vary in appearance across each nail.

Read on to learn more about what these half-moons look like, when their appearance could be cause for concern, and when to see your doctor.

What do healthy lunulae look like?

Healthy lunulae are usually a whitish color and take up a small portion of the bottom of your nail. They’re usually most visible on your thumb.

You may notice that they appear smaller on your pointer finger, gradually shrinking in size until you reach your pinkie where they may be barely visible.

What if my lunulae change color?

Sometimes, the appearance of your lunula or overall nail can be a sign of an underlying condition.

blueblue-graypale bluebrownblackredwhite (whole nail)yellowyellow (whole nail)
Diabetes
Fluoride
Heart failure
Renal disease
Renal failure
Silver poisoning
Terry’s nails
Tetracycline therapy
Wilson’s disease
Yellow nail syndrome

What causes abnormal coloring?

Here are some of the most common reasons for abnormal lunulae:

Tetracycline therapy

Tetracycline medications are antibiotics that are usually used to treat acne and skin infections. Extended use may cause your lunulae to turn yellow.

Diabetes

Pale blue lunulae may be a sign of undiagnosed or uncontrolled diabetes. This is a chronic, lifelong condition that affects the body’s ability to control blood sugar.

Excessive fluoride ingestion

Taking in too much fluoride, like that found in toothpaste, can turn the lunulae brown or black.

Silver poisoning

Blue-grey lunulae may be a sign of silver poisoning.

Yellow nail syndrome

This condition typically produces thick, slow growing nails. The middle of your nail may begin to rise, causing the lunulae to disappear completely. Your entire nail will take on a yellow appearance.

It isn’t clear what causes this syndrome, but it may be tied to:

Terry’s nails

This condition causes the bulk of your nail to appear white, completely erasing the appearance of the lunula. It’s characterized by a pink or red band of separation near the arc of your nails. Although it can happen on one finger only, it usually affects all fingers.

In older adults, this condition is usually a natural sign of aging.

In some cases, it may be a sign of:

Wilson’s disease

This is a rare inherited disorder that occurs when too much copper accumulates in your organs. It’s known to cause blue lunulae.

Severe renal disease

The portion of your nail containing the lunula may turn white, sometimes creating a nail that’s half-brown and half-white. This is sometimes called half-and-half nails and may be a sign of renal disease.

Chronic renal failure

People who experience chronic renal failure may produce more melanin, which can cause your nail bed to turn brown.

Heart failure

If your lunula turns red, it may be a signal of heart failure.

What does it mean if my lunulae are small or missing?

Small or missing lunulae usually aren’t cause for concern. They’re usually just hidden underneath the cuticle or skin at the base of your finger.

In some cases, missing lunulae may be a result of trauma or a sign of:

If you’re experiencing other unusual symptoms, such as fatigue or overall weakness, make an appointment to see your doctor. They can perform a physical exam to help diagnose the cause of your symptoms and advise you on next steps.

What if my lunulae are large?

Researchers don’t know what causes the lunula to take up a significant portion of the nail.

Some reports suggest that lunulae may signal issues with the cardiovascular system, heartbeat disruption, and low blood pressure.

Unscientific theories claim that large lunulae may be common in athletes and people who engage in lots of physical activity. This may be due to the bodily stress associated with high-impact activities, but there is currently no research to back up these claims.

When to see your doctor

Discolored or missing lunulae usually aren’t cause for concern. But if you notice changes in your nail appearance and are experiencing other unusual symptoms, make an appointment to see your doctor.

You should seek immediate medication attention if your hands and feet are also turning blue. This could be a sign of cyanosis, a condition that results from poor circulation or inadequate oxygenation of your blood.

Your doctor can assess your symptoms and advise you on treatment options. Treating the underlying condition will usually restore your nail appearance and improve your overall well-being.