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.
As many as 16 genes influence eye color by determining the amount of melanin inside the specialized cells of the iris. Melanin is the pigment responsible for eye color.
Pigment determines eye color, and a number of genes influence pigment. Brown is the most common eye color worldwide by a large majority. Green is one of the rarest eye colors worldwide.
The iris surrounds the pupil, which is the small black hole in the middle of the eye that helps control how much light enters it.
The iris is the name of the colored part of the eye.
An iris with the least melanin will appear blue. Those with a little more melanin will appear green or hazel, for example.
Eyes that are not brown do not have different color pigments. Instead, they absorb less light because they have less melanin. As a result, they scatter more light, reflecting it along the spectrum of light color.
Melanin is a brown pigment that determines the color not only of someone’s eyes but also of their hair and skin.
As many as 16 genes influence eye color. Most of these genes play a role in the production, transportation, or storage of melanin.
They now know that what determines eye color is more complex.
Scientists used to think that eye color linked to just one gene and that brown eyes were dominant over blue eyes.
The vast majority of people in the world have brown eyes.
The second most common color is blue, but people can also have green, gray, amber, or red eyes.
Some people have eyes that are different colors than each other.
According to estimates, 70–79% of the world’s population have brown eyes, making it the most common eye color worldwide.
In fact, the American Academy of Ophthalmology (AAO) state that everyone on Earth had brown eyes around 10,000 years ago.
Nowadays, the AAO note that about half of those living in the United States, and a higher proportion of people in Africa and Asia, have brown eyes.
People with brown eyes are less likely to develop eye cancer, macular degeneration, and diabetic retinopathy than those with lighter colored eyes.
Brown-eyed people are, however, more at risk of cataracts as they get older.
Blue is the second most common eye color globally, with estimates suggesting that 8–10% of people have blue eyes.
In the U.S., that proportion is higher, at about 27%.
Scientists believe that it is possible to trace all blue-eyed people back to a common ancestor, who likely had a genetic mutation that reduced the amount of melanin in the iris.
Most people with blue eyes are of European descent.
Approximately 5% of the world’s population and 18% of people in the U.S. have hazel eyes, which are a mixture of green, orange, and gold.
Hazel eyes are more common in North Africa, the Middle East, and Brazil, as well as in people of Spanish heritage.
Amber eyes, which have slightly more melanin than hazel eyes but not as much as brown eyes, account for about 5% of the world’s population.
People of Asian, Spanish, South American, and South African descent are most likely to have amber eyes.
An estimated 2% of the world’s population have green eyes, making them very rare overall.
However, green eyes are very common in some parts of the world, including Ireland and Scotland.
In the U.S., where many people descend from ancestors from Ireland and Scotland, about 9% of people have green eyes.
Close to 3% of the world’s population have gray eyes.
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.
People with albinism or ocular albinism usually have little or no melanin in the iris. This lack of pigment causes red or violet eyes.
As eye pigmentation is important for vision, people with ocular albinism often have problems with their eyesight.
A person with ocular albinism may have very blurry vision or poor depth perception. They may experience rapid, involuntary eye movements, have higher light sensitivity, or find that their eyes look in two different directions.
Heterochromia — in which a person has more than one eye color — affects less than 1% of people.
The two eyes might be completely different from one another, or one part of the iris might be different than the rest.
The AAO explain that in people with central heterochromia, the iris has two rings of different colors, while in those with complete heterochromia, one iris is a different color than the other.
Some people are born with heterochromia. In others, an eye injury or health problem might cause it.
More than half of the world's population has brown eyes, making it the most common eye color overall. However, brown is not always the most common when it comes to particular ethnic groups.
Eye color comes from pigmentation in the iris—a muscular tissue that controls the size of your pupil and allows light inside your eye. Inside the iris is a variety of pigments that gives your eyes their color. The combination of pigments and how they are distributed determine your specific hue. All of this comes down to genetics.
This article explains why brown is the most common eye color and how certain eye colors are more common in different groups of people. It also discusses the biological and genetic factors behind eye color.
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Why Your Eyes Are the Color They Are
Eye colors can range from pale blue to dark brown that looks black. The color of your eyes is determined by a combination of pigments in the iris, a two-layer structure that contains clusters of three main pigments: melanin, pheomelanin, and eumelanin.
Melanin, a yellow-brown pigment also responsible for skin tone, is the most predominant one. Even people with blue or green eyes have some melanin in their eyes. People with brown eyes have melanin in both layers of the iris, whereas people with lighter-colored eyes have melanin in the back layer only.
The pigment pheomelanin provides the color for green and hazel eyes. A red-orange pigment, pheomelanin is also responsible for auburn hair. This pigment is most commonly found in people with European ancestry, most notably in Ireland and Scotland.
The darkest pigment is eumelanin, a black-brown hue abundant in dark eyes. The concentration of eumelanin determines the intensity of the eye color. Also responsible for black hair, eumelanin is most abundant in people with African, Asian, Central American, and South American ancestry.
Eye Color Percentages
Brown is the most common eye color in both the United States and the world. More than half of all people have brown eyes. Green eyes are considered to be the rarest—only 2% of all people have them.
Here's a breakdown of the percentages of people in the United States who have each of the various eye colors:
Unusual Eye Colors
Though rare, people can have red or pink eyes or even two different colored eyes.
People who have albinism may not have any pigment in their eyes, so their eye color may be red or pink. This happens because the iris is clear without melanin, allowing blood vessels to show through.
Heterochromia, having two different eye colors, is very rare. Aniridia is a rare condition in which a person is missing part of the iris in one or both eyes.
Genetics of Eye Color
Multiple genes help determine your eye color. Research shows that you cannot predict a baby's eye color based only on the parents' eye colors because many genes are involved.
Genes affect how melanin and other pigments are made, moved, and stored in your body. For example, a protein coded by a gene can influence how much pigment is created by melanosomes (cells that make melanin). If you produce less pigment, then you end up with blue or green eyes.
Genes that are involved in determining your eye color include:
Why Brown Is Most Common
Researchers believe that brown eyes are the most common because our first human ancestors had this eye color. High levels of melanin help to protect the eyes from damaging sun rays.
Brown eyes are more common in people whose ancestors came from hot, sunny climates such as Africa, Asia, and South America. This helped to guard their vision against ultraviolet rays and helped them focus in bright light.
Reasons for Other Eye Colors
Blue and other eye colors developed from a mutation (genetic change). A single ancestor probably had a mutation 6,000 to 10,000 years ago that affected melanin production and resulted in lighter-colored eyes.
Researchers believe that lighter eyes appeared once Early Man left Africa and spread to Europe. These areas had less sunlight, which meant there was less need for melanin.
The reason why someone's eyes look blue has to do with the amount of melanin in the iris. When there is less pigment, there is less light that can be absorbed. The light is scattered and reflects the sky. Eyes that have the smallest amount of melanin are blue.
Other pigments are also at play. Green eyes, for example, have more pheomelanin than melanin. Black eyes have more eumelanin.
Why Eyes Change Color
Many babies are born with blue eyes, but they change color over time. The melanin and other pigments increase in their eyes, changing them and making them darker or lighter within 12 months. The buildup of pigment takes time to develop in babies.
By the time a child reaches the age of three, the eye color is usually permanently set. In some children, this happens even faster and their eye colors are set by nine months.
Eye color doe not typically change after that. If it does, it can indicate a problem. An adult's eyes can change color because of:
If your eye color changes color in adulthood, see an ophthalmologist or other healthcare provider.
Effect on Eye Health
People with certain eye colors are more likely to experience different health conditions.
There are advantages to having brown eyes, such as a lower risk of:
If you are concerned about your eye color or the overall health of your eyes, talk to your eye doctor and get an eye exam.
Which eye color is the rarest?
Green has traditionally been considered the rarest eye color, but grey or violet eyes are even rarer.
Learn More:
What Is the Rarest Eye Color?
Can eyes change color with mood?
Yes. When you experience strong emotions, the body releases different brain chemicals that can constrict or dilate the pupil. This can cause a shift in how eye pigments are dispersed, which can make your eyes look as if they changed color.
What eye color is the most sensitive to light?
Blue eyes are commonly more sensitive to light because they do not have as much melanin to block out UV rays. The lighter the hue of an eye, the more sensitive to light it is. Pale blue or light grey eyes are more sensitive to light than dark blue eyes.
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