Cyanosis
A bluish discolouration of the skin or lips caused by poorly oxygenated blood.
What it means
Cyanosis is a blue or dusky discolouration produced by haemoglobin that is not carrying oxygen. From the Greek kyanos, dark blue.
Two forms, with entirely different significance:
- Central cyanosis — blueness of the lips, tongue and inside of the mouth, meaning the blood leaving the heart is inadequately oxygenated. Always serious.
- Peripheral cyanosis — blueness of the fingers, toes or nail beds only, usually from cold or poor circulation to the extremities. Frequently benign.
In practice
Cyanosis is harder to detect in people with darker skin, and the lips, tongue, gums and nail beds are the more reliable sites to examine.
It is also less apparent in anaemia, because it depends on the absolute amount of deoxygenated haemoglobin — which means a severely anaemic person can be dangerously short of oxygen without looking blue at all.
Why it matters
Blue lips or tongue is a medical emergency. Call 999.
Blue fingers that go white then blue then red on cold exposure suggests Raynaud's phenomenon, which is not an emergency.
This is one of several situations we cannot assess by video and would direct straight to emergency care.
Clinically reviewed by Dr Mohammad Zubair Khan, GMC 7563469
Last reviewed
August 30, 2026