What Is the Most Common Eye Color?

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.

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:

• Brown eyes: 45%
• Blue eyes: 27%
• Hazel eyes: 18%
• Green eyes: 9%
• Other eye colors: 1%

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: 

• OCA2
• HERC2
• ASIP
• IRF4 
• SLC24A4
• SLC24A5
• SLC45A2
• TPCN2
• TYR
• TYRP1

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:

• Genetics
• Trauma
• Illness
• Sun damage
• Medications

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:

• Macular degeneration
• Diabetic retinopathy
• Eye cancer

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.