A blue skin tone can be caused by methemoglobinemia where an excess of methemoglobin (a form of haemoglobin that contains ferric iron rather and ferrous iron and is useless or very poor at carrying oxygen in the blood) builds up. This can occur if there is a deficiency in the enzyme called cytochrome-b5 methemoglobin reductase which converts methemoglobin into haemoglobin.
Normally, people have less than 1 percent of methemoglobin. Between 1 and 10 percent does not have much effect and levels greater than 20 percent tends to cause heart abnormalities, seizures and even death. But at levels of between 10 and 20 percent a person can develop blue skin without any other symptoms.
Incidences of methemoglobinemia are extremely rare, but do occur and one family in particular is on record as having been seriously affected.
Martin Fugate came to Troublesome Creek in eastern Kentucky from France in 1820 and family folklore says he was blue. He married Elizabeth Smith, who also carried the recessive gene. Of their seven children, four were reported to be blue.
There were no railroads and few roads outside the region, so the community remained small and isolated. The Fugates married other Fugate cousins and families who lived nearby, with names like Combs, Smith, Ritchie and Stacy.
Benjamin Stacy, born in 1975, is the last known descendent of the Fugates to have been born exhibiting the characteristic blue color of the disease, but lost his blue skin tone as he grew older. Benjamin "Benjy" Stacy so frightened maternity doctors with the color of his skin "as Blue as Lake Louise" that he was rushed just hours after his birth in 1975 to University of Kentucky Medical Center.
As a transfusion was being readied, the baby's grandmother suggested to doctors that he looked like the "blue Fugates of Troublesome Creek." Relatives described the boy's great-grandmother Luna Fugate as "blue all over," and "the bluest woman I ever saw."
The most detailed account, "Blue People of Troublesome Creek," was published in 1982 by the University of Indiana's Cathy Trost, who described Benjy's skin as "almost purple."
The disorder can be inherited, as was the case with the Fugate family, or caused by exposure to certain drugs and chemicals such as anesthetic drugs like benzocaine and xylocaine. The carcinogen benzene and nitrites used as meat additives can also be culprits, as well as certain antibiotics, including dapsone and chloroquine.
Dr. Ayalew Tefferi, a haematologist from Minnesota's Mayo Clinic. Is reported to have described methemoglobinemia patients' lips as being purple, their skin as being blue and their blood as "chocolate colored" because it is not oxygenated.