Blue nails: what are the causes and when should we worry?


Blue fingernails may indicate that the blood is not carrying enough oxygen to the fingertips. There are many possible causes, some of which are serious. Therefore, a person with blue nails should see a doctor to determine the underlying cause.

In some cases, the nails turn blue or purplish due to cyanosis, which can also affect lips and skin. Cyanosis can occur if the blood does not carry enough oxygen to the fingertips or if the person has poor blood circulation. It can also result from problems with hemoglobin, a protein in red blood cells that is responsible for carrying oxygen. Various health conditions that affect the respiratory and cardiovascular systems can also cause cyanosis. A person who notices they have blue toenails should contact a doctor for advice to rule out any underlying medical conditions.

This article looks at conditions that can cause blue toenails and explains how doctors diagnose and treat cyanosis. It also addresses the question of when a person should seek help.

Why do fingernails turn blue?

If only one fingernail is blue, this is most likely due to an injury resulting in blood pooling under the nail. When all the nails are blue, it indicates cyanosis, which is a symptom of another condition rather than a condition on its own. Blue nails are caused by a lack of oxygen in the blood.

Blue nails can also occur if the circulatory system does not transport blood through the body as it should, which results in poor circulation and a blue tint. The cold can temporarily cause poor circulation, as blood vessels narrow due to the drop in temperature. They do this to prevent blood from reaching the extremities and to keep internal organs at an optimum temperature. If low temperature is the cause, normal nail color should return when the person warms their hands.

Possible Causes of Blue Nails

Blue nails indicate that the fingers, toes or both are not getting enough oxygen.

The following causes can cause cyanosis:

Lung diseases

Various lung diseases can lead to blue discoloration of the nails. These conditions include:

Chronic Obstructive Pulmonary Disease (COPD)

COPD is an umbrella term for a group of lung diseases progressive, including emphysema and chronic bronchitis. Emphysema destroys the air sacs in the lungs, while bronchitis causes the bronchial tubes to become inflamed and narrow, leading to mucus buildup. Approximately 30 million people live with COPD in the United States.

L ‘asthma

Asthma causes the airways to narrow and swell and can also increase the production of mucus, which can lead to buildup. People with asthma may have difficulty breathing, chest pain, coughing and wheezing which can interfere with their daily life. Sometimes asthma can lead to life-threatening asthma attacks.

Acute respiratory distress syndrome

People with ARDS have difficulty breathing, and their breathing rate and heart rate are faster than normal, which leads to a drop in oxygen in the blood. Doctors treat ARDS with oxygen therapy to improve blood oxygen levels.


Bacteria, viruses and fungi can all cause pneumonia, which is an infection of the lungs. Following a severe flu infection, for example, pneumonia may develop. Symptoms can range from mild to severe, but most people recover from pneumonia in 1 to 3 weeks.

Pulmonary Embolism (PE)

If one of the arteries in the lungs is blocked by a blood clot, this can cause PE. Usually the clot comes from a leg or other part of the body and blocks blood flow to the lungs, thus becoming life-threatening.

Heart disease

Some cases of blue toenails may be due to heart disease, for example:

Congenital heart disease

Babies can be born with abnormal hearts and blood vessels. Although some cases are asymptomatic, others cause life-threatening symptoms.

Eisenmenger syndrome

This rare disease affects the heart and lungs and is often a late complication of congenital heart disease. Eisenmenger syndrome causes high blood pressure and abnormal circulation of blood in the heart.

Congestive heart failure

L heart failure causes problems with the heart, which is unable to pump blood as it should. Symptoms include shortness of breath, extreme fatigue and swelling in the extremities.

Blood cell and vessel abnormalities

Some Blood cell and vessel issues can also cause blue nails. These include the following problems


This condition causes an increase in the level of methemoglobin, a form of hemoglobin which cannot release oxygen. This condition can be present from birth or develop as a result of exposure to certain chemicals or medications such as antibiotics and local anesthetics.

carbon monoxide

Carbon monoxide blocks the ability of hemoglobin to bind oxygen.

Polycythemia vera

This form of blood cancer causes the bone marrow to produce too many blood cells.

Raynaud’s phenomenon

People with this disease experience decreased blood flow in the hands and feet due to spasm of blood vessels.

Diagnosis and treatment of nails blue

A doctor will diagnose cyanosis by performing a physical exam to examine blue fingernails and check for clubbed fingers. Cloverleaf fingers can indicate congenital heart disease and lung problems. The doctor may also assess the person for cardiac or respiratory symptoms.

Blood oxygen tests are an essential aid in the diagnosis of cyanosis. A doctor will draw blood to measure arterial blood gas (ABG), which indicates blood oxygen and hemoglobin levels. He may also place a device called a pulse oximeter on the person’s finger to measure blood oxygenation. These tests help determine why a person has blue fingernails.

As cyanosis is a symptom of an underlying condition, the goal is to treat the cause.

When to seek help

It is not uncommon for fingernails to appear blue in cold weather, but should return to their normal color once the person warmed up. If blue nails are probably not due to low temperature and the color persists, it is important to see a doctor. Doctors will identify and correct the underlying cause of cyanosis and treat it to restore optimal blood flow in the body. Receiving treatment quickly should limit the possibility of possible complications and improve the person’s outcome.

If a person with blue nails also has symptoms such as chest pain, shortness of breath, profuse sweating and dizziness, she must immediately call the emergency services. These symptoms may indicate a medical emergency.


Adeyinka, A., et al. (2021). Cyanosis.

ARDS symptoms and diagnosis. (2020).

Blue skin or lips (cyanosis). (2020).

Eisenmenger syndrome. (93).

Ludlow, JT, et al. (2020). Methemoglobinemia.

Pahal, P., (2021). Central and peripheral cyanosis.

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