Bluish or livid color of the skin and the mucous membranes due to low oxygen content of the blood.

This is particularly conspicuous in the lips and nails. Cyanosis can appear in various medical conditions, for which the underlying course is low oxygen saturation of the blood, as for example lung diseases, heart defects, in high geographic regions and more.

Cyanosis in inner parts of the lips (that are not exposed to cold), cheeks, tongue and conjunctiva of the eyes, can evidence reduced oxygen saturation of blood secondary to pulmonary or cardiac disease.

Cyanosis appearing in external parts only, such as finger tips, the tip of the nose or the outer parts of the lips can be due to decreased blood flow into the skin because of its exposure to low temperature.