Blue Eyes: How Rare Are They?

You almost certainly know someone with blue eyes — maybe you have those "baby blues" yourself. Blue is the second most common eye color in the United States, just behind brown. But the story of how blue eyes happen is one of the most surprising in all of human genetics.

How rare are blue eyes?

About 27% of the US population has blue eyes, according to a 2014 poll by the American Academy of Ophthalmology. So they're not the rarest color, but they're far from the most common — and the share varies enormously by region. In Scandinavian countries and Iceland, blue eyes are everywhere; in much of the world they're genuinely uncommon.

What causes blue eyes?

Here's the twist: blue eyes aren't actually blue. There's no blue pigment in them at all. Like every eye color, they come down to melanin — the same pigment that colors skin. Blue eyes simply lack melanin in the front layer of the iris. When light hits that low-pigment layer, it scatters and reflects more blue light back out — the very same effect that makes the sky look blue.

Where do blue eyes come from?

Originally, blue eyes were a mutation of brown eyes. For most of human history, brown was the only eye color. Genetic research traces blue eyes to a single mutation that appeared roughly 6,000 to 10,000 years ago in an individual in northern Europe — a change that essentially "switches off" the iris's ability to make melanin. Everyone with blue eyes today shares that distant common ancestor; the trait has been passed down through several genes ever since.

That's also why genetics can surprise you: two blue-eyed parents won't always have a blue-eyed child, and brown-eyed parents often do.

A few fun facts

• "Baby blues" are real: many babies are born with blue eyes and develop more melanin — and a different color — as they grow.
• Light tolerance: with less melanin, blue eyes let more light through, so they can handle low light well — but they also tend to be more sensitive to bright light, so sunglasses are your friend.
• The "attractiveness" myth: people say blue eyes are especially attractive, but when researchers had the same people rate eyes blind to color, the link mostly disappeared — it seems more cultural than real.

Getting the blue-eye look

• Choose your blue: soft sky and gray-blue read most natural; bright sapphire or "ice" blue make a statement.
• On dark eyes, pick an opaque blue so the color fully covers your natural brown.
• On light eyes, a translucent blue deepens and brightens what you already have.

Eye-color statistics: American Academy of Ophthalmology. General information, not medical advice.