Brown is the most common eye color worldwide by a large majority. In contrast, green is one of the rarest eye colors worldwide. The color of the eyes depends on how much melanin the eyes contain.

Melanin is a brown pigment that gives skin its color, as well as the eyes. As many as 16 genes influence the amount of melanin inside the specialized cells of the iris.

In this article, we explain what eye color is and what causes it. We also take a look at the breakdown of the proportion of people around the world with each eye color.

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The colored part of the eye is known as the iris, which contains pigments that determine a person’s eye color.

Eye color is largely genetic. As many as 16 genes dictate what a person’s eye color will be. Most of these genes play a role in the production, transportation, or storage of melanin. Melanin is a brown pigment that determines the color not only of someone’s eyes, but also their hair and skin.

The more melanin in the eyes, the browner they are. Eyes that are not brown do not have different color pigments. Instead, they have less melanin. An iris with the least melanin will appear blue, while those with a little more melanin may appear green or hazel.

Scientists used to think that just one gene determined eye color, and that brown eyes were dominant over blue eyes. They now know that what determines eye color is more complex.

The vast majority of people in the world have brown eyes. The second most common color is blue, but people can also have hazel, green, or gray eyes.

Brown eyes

According to a 2020 study, 79% people worldwide have brown eyes, making brown the most common eye color.

It may also be one of the oldest eye colors in humans. Around 10,000 years ago, everyone on Earth had brown eyes. The melanin helps protect the eyes from the sun, which is why brown eyes are most common in countries in Africa and Asia.

People with brown eyes may be less likely to develop eye cancer, macular degeneration, and diabetic retinopathy than those with lighter eyes. However, brown-eyed people may be more at risk of cataracts as they get older. The reasons for this are unclear.

Blue eyes

Blue is the second most common eye color globally, with estimates suggesting that 8 to 10% of people have this eye color. In the U.S., that proportion is higher, at about 27%. In countries such as Iceland, blue is the majority eye color.

All people with blue eyes share the same genetic trait, meaning they likely descend from one common ancestor.

Hazel

Approximately 5% of the world’s population and 18% of people in the U.S. have hazel eyes. Hazel eyes are a mixture of green and brown, but can also contain amber or gold hues.

Green

Around 2% of the world’s population have green eyes, making them very rare overall. In the U.S., about 9% of people have green eyes.

Gray

Globally, gray is a rare eye color.

People with gray eyes have little or no melanin in their irises, but they have more collagen in a part of the eye called the stroma. The light scatters off the collagen in a way that makes the eyes appear gray.

Red or violet

Humans do not naturally have red or violet eyes. Occasionally, though, people with albinism can appear to have red or violet eyes in certain lights. This is a product of light hitting blood vessels at the back of the eye.

As eye pigmentation is important for vision, people with ocular albinism can have visual symptoms, such as:

  • blurry vision
  • reduced depth perception
  • longsightedness or nearsightedness
  • rapid, involuntary eye movements (nystagmus)
  • light sensitivity (photophobia)
  • problems with the macula, or center of the retina

Multiple colors

Heterochromia, in which a person has more than one eye color, is uncommon. There are no up-to-date statistics on how prevalent it is globally.

In heterochromia, the two eyes might be completely different from one another, or one part of the iris might be different than the rest. If the inner and outer rings of the iris are different, a person has central heterochromia. If each eye is completely different in color, a person has complete heterochromia.

Some people are born with heterochromia. In others, an eye injury or health problem might cause it.

Yes, under certain circumstances.

Babies often have changes in eye color over the first few months of life. Some have blue or gray eyes at birth, which then change to their permanent eye color as pigment builds up. By 9 months, most babies have the eye color they will have for the rest of life.

People with certain health conditions can also notice a change in the color of their eyes over time. Otherwise, though, eye color rarely changes in adults. For most, the only way to achieve this is with colored contact lenses.

People can develop heterochromia at any point in their life. Possible causes include:

  • eye injury
  • diabetes
  • swelling due to iritis or uveitis
  • Fuchs’ heterochromic cyclitis
  • glaucoma
  • acquired Horner’s syndrome
  • ocular melanosis
  • iris tumor
  • Posner-Schlossman syndrome
  • Chediak-Higashi syndrome

The AAO advise anyone who notices a color change in one or both eyes to speak to a doctor.

At least 16 genes play a part in determining someone’s eye color.

Brown eyes have the highest amount of the pigment melanin in the iris, and are the most common worldwide. Scientists believe that it was the only eye color up until about 10,000 years ago.

Lighter color eyes have less melanin. This reduced pigmentation affects how they reflect light and can make them appear blue, green, or hazel.