A low level or lack of oxygen circulating in your red blood cells can cause blue fingernails. Other causes can include chronic conditions and cold temperatures.

This condition is known as cyanosis. It occurs when there isn’t enough oxygen in your blood, making the skin or membrane below the skin turn a purplish-blue color.

The skin discoloration could also mean that there’s a high level of an atypical form of hemoglobin in your blood. Hemoglobin is the protein responsible for transporting oxygen in your blood.

Cold temperatures can also cause your fingernails to turn blue. That’s because cold temperatures force your blood vessels to constrict. The narrow pathways make it difficult for enough oxygen-rich blood to get to your nails.

If your usual nail color returns upon warming up or massaging your hands, the blue color may have been due to that part of your body not getting enough blood supply because of cold temperatures.

Blue fingers due to cold temperatures is a common response of the body to keep internal organs at the right temperature.

However, if fingernails remain blue, there may be an underlying condition or structural difference interfering with the body’s ability to deliver oxygen-rich blood.

Learn more about causes, treatment, and when to get help.

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Erica Singleton

Health conditions involving the lungs, heart, blood cells, or blood vessels can cause the blue discoloration in your fingernails. Conditions that can cause cyanosis include the following:

Diseases of the lungs

Diseases of the heart

Atypical blood cells

Atypical blood vessels

A noninvasive pulse oximeter is the simplest way to measure the oxygenation of blood. Doctors draw arterial blood gases to measure how much oxygen is in your blood. This helps determine what factors might be contributing to blue fingernails.

Treatment involves first identifying the underlying cause to restore adequate oxygen to the blood.

Blue fingernails, or cyanosis, occur when your blood doesn’t have enough oxygen. It is most often caused by cold temperatures.

Occasionally, it can be caused by medical conditions. These include diseases of the lungs or heart, or atypical blood cells or vessels.

The diagnosis is typically noninvasive, and treatment depends on the underlying cause.