The colored part of your eye is called the iris. The color comes from a brown pigment called melanin. It’s the same pigment that causes skin color. Different eye colors are caused by different amounts of pigment.

Today, brown is the most common eye color worldwide.

Scientists think that long ago when everyone lived in hot climates where it was sunny year-round everyone had brown eyes. Dark irises may have protected their eyes from being damaged by ultraviolet radiation and bright sunlight.

As people moved north, sun damage was less of a problem. Eye color became lighter, which may have made it easier to see better during the cold, dark winters.

Europeans have the widest variety of eye colors. Their eyes range from dark brown to light blue. In general, they have the lightest eye colors.

Hazel, green, and blue eyes are common in Central and South America and some parts of the Middle East.

According to World Atlas, eye color tends to fall into these percentages:

Brown

  • Between 55 and 79 percent of people worldwide have brown eyes.
  • Brown is the most common eye color.
  • Dark brown eyes are most common in Africa, East Asia, and Southeast Asia.
  • Light brown eyes are found in West Asia, the Americas, and Europe.

Blue

  • Between 8 and 10 percent of people worldwide have blue eyes.
  • Blue eyes are most common in Europe, especially Scandinavia.
  • People with blue eyes have the same genetic mutation that causes eyes to produce less melanin.
  • The mutation first appeared in a person living in Europe about 10,000 years ago. That individual is a common ancestor of all blue-eyed people today.
  • You might see better at night if you have blue eyes, but you might also have more trouble with glare.

Green

  • About 2 percent of people have green eyes.
  • Green eyes are most common in Northern, Central, and Western Europe.
  • About 16 percent of people with green eyes are of Celtic and Germanic ancestry.
  • The iris contains a pigment called lipochrome and only a little melanin.

Hazel

  • Approximately 5 percent of people have hazel eyes.
  • Hazel eyes are uncommon, but can be found throughout the world, especially in Europe and the United States.
  • Hazel is a light or yellowish-brown color with specks of gold, green, and brown in the center.
  • People with hazel eyes have almost as much melanin as those with brown eyes, but it’s mostly around the edge of the iris instead of the center.

Amber

  • About 5 percent of people around the world have this rare eye color.
  • Amber eyes are uncommon, but can be found throughout the world.
  • Amber is a golden yellow or coppery color without specks of gold, green, or brown.
  • The iris contains mostly the pigment lipochrome and not much melanin.
  • Amber eyes are a lot more common in dogs, fish, and birds.

Gray

  • Less than 1 percent of people have gray eyes.
  • Gray eyes are very rare.
  • Gray eyes are most common in Northern and Eastern Europe.
  • Scientists think gray eyes have even less melanin than blue eyes.
  • Gray eyes scatter light differently, which makes them pale.

Heterochromia

If you have heterochromia, all or part of one of your irises is a different color than the other one. This condition is seen in less than 1 percent of people, but it’s frequently seen in dogs. It can be the result of:

  • heredity
  • problem during eye development
  • an eye injury
  • a medical condition

Scientists used to think your eye color was determined by two eye color genes, one from each parent. Since brown is dominant over blue, a blue-eyed person would have two blue eye genes, and two blue-eyed parents couldn’t have a brown-eyed child.

We now know that it’s much more complicated than that. Your eye color is determined by several genes that control melanin production in your iris. Darker eyes have a lot of melanin, while light eyes have only a little.

Melanin absorbs light. When an object absorbs light, it looks dark. But when it doesn’t absorb light, the light is reflected and the object is the color of the light it reflects. Light reflected from your eye is from the blue part of the color spectrum.

Brown eyes have a lot of melanin, so they absorb light, which makes them dark. Hazel eyes have less melanin than brown eyes, but more than green eyes. Blue eyes have the least amount of melanin and reflect the most light.

Because you inherit genes from your parents, it’s likely that your eyes will be similar in color to one or both of your parents. But it’s also possible for you to have brown eyes, even if both of your parents have blue eyes.

Because eye color is due to reflected light, blue, green, and even hazel eyes can change a little in different lighting conditions. However, once your eye color is set in childhood, your eyes can’t naturally change to a completely different color.

Babies are the exception. Most are born with blue or gray eyes, as melanin production in the eyes doesn’t begin until age 1. By age 3, most children have the eye color they’ll have the rest of their life.

You can artificially change your eye color in two ways, but both options may have risks.

Contact lenses

With contact lenses, you can accentuate, enhance, or completely change your eye color. These lenses come in a wide variety of colors and can correct vision or not.

Learn about potential problems caused by colored contact lenses here.

Iris implant

A surgical procedure originally developed to treat eye injuries and other conditions, the iris implant has been used to permanently change eye color. In 2014, the American Academy of Ophthalmology warned against undergoing this procedure.

Read more about the iris implant and colored contacts here.

Some medical conditions are known to affect eye color. They don’t permanently change the color of your iris. Instead, they usually affect the whites or cornea of your eye. These conditions include:

  • Albinism. In this condition, your eyes don’t produce enough melanin. If the condition is mild, you usually have light blue or violet eyes. But if the condition is severe, you have little to no melanin. Your eyes appear pink or red because the blood vessels in your eye show through. The condition also causes severe vision issues. It may affect the pigment in your eyes, hair, and skin, or it can affect only your eyes.
  • Anisocoria. This is when one of your pupils is larger than the other. Because the iris in the eye with the bigger pupil is smaller, it looks darker than the other. Some people are born with this condition. For those individuals, the size difference is small. The difference is bigger when the cause is a stroke, brain injury, or eye trauma. Sudden-onset anisocoria should be evaluated right away.
  • Arcus senilis. This is when cholesterol builds up and forms a hazy white or blue ring around your cornea. It’s harmless and more common as you age.
  • Hepatitis and other liver disease. When your liver is inflamed or damaged, it can’t remove bilirubin, so it builds up in your blood. This makes the whites of your eyes and skin yellow.
  • Hyphema. This is blood inside of your eye, usually due to an injury or following surgery.
  • Uveitis. This is inflammation inside your eye. It’s caused by infection, injury, or exposure to toxins. It makes the white part of the affected eye look red. This condition requires immediate medical attention.

Common eye diseases occur less often in people with brown eyes than with gray, green, or blue eyes. This may be because melanin is protective.

For example, a 2001 study found that type 1 diabetes was more common in people of northern European descent with blue eyes. This may be why diabetic retinopathy is more common in people with light-colored eyes.

Other conditions associated with light-colored eyes include:

Eye color may also be associated with how you experience pain.

A 2011 study found women with light-colored eyes, such as blue or green, experienced less pain when giving birth compared to women with dark eyes, such as hazel or brown. They also had less depression, negative thoughts, and anxiety.

However, another study found eye color made no difference in the amount of pain women experienced when getting a dental injection.

Your eye color is determined by the amount of melanin in the iris. Brown eyes have the most melanin and are the most common color. The lower the amount of melanin in your eyes, the lighter they will be.

Your eye color is permanently set around age 3. There are some ways to artificially change your eye color, but they can damage your eyes. Be sure to thoroughly research anything you’re considering doing to change your eye color.