The red pigment in blood is known as haemoglobin and is responsible for binding to oxygen and carrying it around the body. Haemoglobin with oxygen attached is bright red in colour and gives us the red colouring of our lips, gums and tongue. Haemoglobin without oxygen turns blue. If breathing is inefficient and sufficient oxygen cannot get through the lungs to bind to haemoglobin, then the lips and tongue may appear blue. This blue discolouration is called cyanosis.

Cyanosis can occur in the fingers due to cold weather and is known as peripheral cyanosis. This is not a sign of inefficient breathing unless the lips and tongue are also discoloured (central cyanosis), but instead may simply reflect the cold weather. Central cyanosis is always significant and should be looked for during an assessment of breathing. If you see central cyanosis, the casualty is not able to get enough oxygen into the body and you need help urgently. Lack of oxygen is known as hypoxia and hypoxic people can die.