Methemoglobinemia, also known as "met-H", is a usually genetic blood disorder characterized by the presence of a higher than normal level of methemoglobin in the blood.

Due to an enzyme deficiency, the blood of met-H victims has reduced oxygen-carrying capacity. Instead of being red in colour, the arterial blood of met-H victims is brown. This results in the skin of Caucasian sufferers gaining a bluish cast. Hereditary met-H is caused by a recessive gene. If only one parent has this gene offspring will have normal-hued skin, but if both parents carry the gene there is a chance the offspring will have blue-hued skin.

Acquired methemoglobinemia can be caused by the use of nitrate-containing drugs, such as nitroglycerin.

External links

• Article on the Fugates of Appalachia, an extended family of blue-skinned people