Some time around the year 1800, a man named Martin Fugate made his way to eastern Kentucky, smack in the middle of the Appalachian Mountains. He married a woman named Mary. They had children, as couples often do. So did a nearby couple — Robert Smith and his wife, Alicia Combs. Some of the Fugate children ended up marrying some of the Smith children, and they, too, had children.

Some of their children were blue.

These blue people, a handful pictured above in what is apparently a family portrait, were a byproduct of a coincidence of reccessive genes meeting, and, after that, intermarriage and inbreeding. Mary Fugate was a carrier of a hereditary disease known as methemoglobinemia, or, for short, met-H. So was someone on the Smith/Combs side. Met-H is recessive, so in order to be anything other than a carrier, both parents need to have the gene, and in the case of subsequent Fugates, that’s exactly what happened. Over the next fifty or so years, the isolated Appalachian families carried on their lineage in a straight-line-ish family tree, with a large amount of inbreeding relative to the rest of the United States (but probably typical for Appalachia at the time). A few children were born with met-H, a disease which causes blood to have a higher than normal level of methemoglobin, and therefore, a reduced ability to carry oxygen. In turn, those afflicted with met-H have darker looking blood and many Caucasian ones therefore also have off-colored skin, typically with a blue hue to it. And the gene pool, undisturbed, yielded generation after generation of blue-tinted people.

The Blue Fugates, as they’d later be known, were first discovered by the medical community in 1958, according to a report from the Tri City Herald, but it would not be until the 1980s that science found a treatment . According to an article in Science magazine, the treatment is entirely counter-intuitive — it involves drinking blue dye. Specifically, the afflicted person drinks a chemical compound called methylene blue which, when dissolved in water, turns into a blue solution (as seen on its Wikipedia entry). The methylene blue acts as an “electron donor,” converting the methemoglobin into regular (red) hemoglobin, and thereby turning the person’s skin to the typical hue, quite literally right before their eyes. Unfortunately, the effect of the methylene blue is temporary, requiring daily doses to keep the blue away.

But with Appalachia modernizing and the gene pool expanding, this probably will not matter much longer. It is likely that hereditary blueness due to met-H is going to become even more rare.

Bonus fact : Even if met-H disappears, we will still have some blueness out there — specifically, due to what’s called the Mongolian blue spot. Seen here on a baby girl’s rear, the “spot” is actually a birth mark common to Mongolians and others. It typically disappears by age five and rarely remains after puberty.

From the Archives: Pale Blue Dot: In a sense, we’re all blue.

Related: You can buy methylene blue on Amazon — but it’s for fish tanks, not for blue-hued people.