Blue fingernails are caused by a low level or lack of oxygen circulating in your red blood cells. 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 abnormal 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 normal nail color returns upon warming up or massaging your hands, the blue color was likely due to that part of your body not getting enough blood supply because of cold temperatures.

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

However, if fingernails remain blue, there may be an underlying disease or structural abnormality interfering with the body’s ability to deliver oxygenated red blood.

Blue discoloration of your fingernails can be caused by problems in the lungs, heart, blood cells, or blood vessels. Conditions that can cause cyanosis include:

Diseases of the lungs

Diseases of the heart

Abnormal blood cells

Abnormal blood vessels

A noninvasive pulse oximeter is the simplest way to measure the oxygenation of blood. Arterial blood gases (ABGs) are drawn 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 in order to restore adequate oxygen to the blood.

Call 911 if your blue fingernails are accompanied by:

  • shortness of breath, breathing difficulties, or gasping for air
  • chest pain
  • profuse sweating
  • dizziness or fainting