In the movie Avatar (2009) the protagonists are forest-loving beings with intense blue skin. This is a fictitious feature and completely isolated from normal in humans. However, there is a rather unusual genetic disorder that can cause people to be born with a dark bluish hue: it is methemoglobinemia, the disease of blue skin.
Methemoglobinemia is a blood disorder in which an excessively high amount of methemoglobin, a type of hemoglobin, is produced. Hemoglobin is the molecule in red blood cells that is responsible for distributing oxygen throughout the body.
When methemoglobinemia occurs, hemoglobin is unable to deliver oxygen effectively to body tissues. That is why people with this disorder have chocolate-colored blood and blue skin. However, for a person to have this genetic disease, both parents must pass the recessive gene for the disorder.
The Fugate family
The most popular case of methemoglobinemia comes from a family that lived in isolation for six generations in the hills of Kentucky, United States. The family began with a man of French origin named Martin Fugate, who married Elizabeth Smith, of Appalachian descent from the area. Both were unknowingly carriers of the recessive gene for the disorder. Thus, the Fugate family had seven children, four of whom had blue skin.
Despite having this genetic disorder, most family members lived into their 80s and 90s without major health problems. Normally, people have less than 1% methemoglobin in their blood. When those levels rise to more than 20% it can cause heart abnormalities, seizures and even death. But at levels between 10 and 20% a person can have blue skin and not present any other symptoms.
Other causes of blue skin
In addition to the genetic factor, methemoglobinemia can be caused by taking certain medications and chemicals, such as benzocaine and xylocaine. It can also be produced by some meat additives and certain antibiotics, such as chloroquine and dapsone.
The skin can also turn blue due to silver poisoning, better known as argyria. Argyria is a disease caused by long-term exposure to silver, and the most common symptom is that the skin turns a bluish-gray color. Before the advent of antibiotics, people used silver nitrate and colloidal silver to treat infections.
