The coloured part of your eye is called the iris. Its colour comes from melanin, the same pigment that determines skin colour. Different eye colours are the result of varying amounts of melanin.
Today, brown is the most common eye colour worldwide.
According to the American Academy of Ophthalmology (AAO), at one time, all humans had brown eyes. Then, a common ancestor experienced a gene change that led their descendants’ eyes to produce less melanin.
Melanin can protect the eyes from sun damage. That may explain why brown eyes are more common in hotter climates throughout Asia and Africa.
What are eye colour percentages around the world? Determining the number of people with a certain eye colour is challenging.
Researchers have changed the colour categories over time. Some have included grey, blue, brown, and black, while others have also used categories like pale yellow and deep yellow.
A 2015 Canadian study on eye colour in young adults noted that there has been little research on the genetic basis of eye colour in people of non-European ancestry. The authors also stated that although brown eyes are dominant outside of Europe, there’s extensive variation within that brown colour.
“Brown” eyes can range from a light reddish-yellow to a dark brownish-black.
Over 50% of the world’s population has brown eyes, according to the AAO. Just around 2% of people worldwide have green eyes.
In the United States One 2014 survey asked over 2,000 people in the United States about their eye colour. According to the AAO, the survey data can be used to determine eye colour prevalence across the country at large.
Brown is the most common eye colour in the United States, just as it is globally. Here’s the breakdown of eye colour prevalence in the United States:
45% of people with brown eyes 27% with blue eyes 18% with hazel eyes 9% with green eyes 1% with eyes of another colour
In Africa Most people of African descent have brown eyes, according to a 2021 literature review.
In South Asia and East Asia The 2015 study mentioned earlier found that almost all study participants representing South Asia and East Asia had brown eyes.
Participants were categorised as South Asian if all of their grandparents had Bangladeshi, Indian, Pakistani, or Sri Lankan ancestry. East Asian participants had grandparents with Chinese, Japanese, Korean, or Taiwanese ancestry.
There was slightly more eye colour variation among South Asian participants than East Asian participants. Few East Asian participants had green eyes, while none had blue eyes.
Other research has also concluded that most Asian people have brown eyes.
In Europe and Central Asia A 2019 literature review on eye and hair colours included data on eye colours for countries across Europe and Central Asia. The review used the broad categories of “brown,” “intermediate,” and “blue.”
How is eye colour determined? Scientists used to think your eye colour was determined by two eye colour genes, one from each parent. Since the gene for brown is dominant over blue, the belief was a blue-eyed person would have two genes for blue eyes, and two blue-eyed parents couldn’t have a brown-eyed child.
We now know that it’s much more complicated than that. According to an older 2010 study, your eye colour is determined by up to 16 genes that control melanin production in your iris.
Melanin absorbs light. When an object absorbs light, it looks dark. When it doesn’t absorb light, the light is reflected, and the object is the colour of the light it reflects. Light reflected from your eye comes from the blue part of the colour 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, your eyes will likely be similar in colour to their eye colours. It’s also possible for you to have brown eyes even if both of your parents have blue eyes.
Can you change your eye colour? Because reflected light determines eye colour, blue, green, and hazel eyes can look slightly different under different lighting conditions. However, once your eye colour is set in childhood, your eyes can’t naturally change to a completely different colour.
Babies are the exception. Melanocytes, which are specialised cells that secrete melanin, are most active in the first year of life. This means eye colour is usually determined by age 1 year. However, changes in eye colour begin to slow down once a baby reaches 6 months old.
You can artificially change your eye colour, but it can be risky.
Contact lenses You can accentuate, enhance, or completely change your eye colour with contact lenses. Decorative, or costume, lenses come in a variety of colours and can correct vision or not.
Note that it’s illegal to sell contact lenses, even decorative lenses, without a doctor’s prescription in the United States.
Some hazards of wearing lenses that a doctor hasn’t prescribed or are otherwise ill-fitting include:
cuts and scratches on the eye eye infection an ulcer on the cornea, the dome-shaped front layer that bends light so the eye can focus corneal abrasion reduced oxygen flow to the eye If you want to try coloured contacts, see an optometrist first. They can guide you to a safe and healthy pair of coloured contacts to enhance your look.
What’s the takeaway? The amount of melanin in your iris determines your eye colour. The less melanin you have in your eyes, the lighter they’ll be. Brown eyes have the most melanin and are the most common worldwide.
Researchers continue to learn more about eye colour, including the wide range of iris hues. Certain iris colours may come with certain health risks. As experts learn more, people may be able to use this knowledge to improve their overall health.
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