Eye color is determined by the amount and type of pigment in the iris of the eye. The two main pigments that determine eye color are melanin and lipochrome. Melanin is a dark brown pigment and lipochrome is a light yellow pigment. The combination and ratio of these two pigments determine the iris color. Human eye color can range from the darkest shades of brown to the lightest tints of blue and green. But some eye colors are rarer than others. So which eye color is the rarest in humans?
Common Eye Colors
Here are some of the most common eye colors from most to least common:
| Brown | Around 55% of the global population |
| Blue | Around 27% of the global population |
| Hazel | Around 8% of the global population |
| Green | Around 2% of the global population |
| Gray | Around 1% of the global population |
As you can see, brown eyes are by far the most common eye color worldwide. After brown, blue eyes are the next most prevalent, followed by hazel, green, and gray eyes. But there are some even rarer eye colors that occur in less than 1% of the population.
Rare Eye Colors
Here are some of the rarest eye colors found in humans:
Amber Eyes
Amber eyes are a solid golden or copper color without any other colors mixed in. This is one of the rarest eye colors in the world, only appearing in about 0.05% of the global population. Amber eyes are thought to be a genetic mutation that causes a lack of melanin in the eyes. They are most common in parts of Asia and South America.
Red/Violet Eyes
Eyes with a reddish or violet hue are also extremely rare. They are thought to occur in less than 0.05% of people worldwide. True red or violet eyes have a rich burgundy or reddish-purple color throughout the iris. This eye color is believed to be caused by very low levels of melanin as well as a thinning of the iris muscle, allowing more light to pass through and produce a red color.
Heterochromia
Heterochromia refers to eyes that have two different colors in the same iris or eyes that are different colors from each other. Complete heterochromia, where one iris is a different color from the other, is very rare, occurring in only about 0.06% of the population. Segmental heterochromia, where part of the same iris is a different color, is slightly more common at around 1% of people. Either type is considered one of the rarest eye variations.
Black Eyes
Eyes that are completely black with no distinction between the pupil and iris are extremely rare. The medical term for black eyes is aniridia. This condition is caused by a complete lack of iris tissue due to a genetic mutation. It affects less than 0.00001% of the global population. Those with aniridia usually have extremely poor vision.
Geographic Distribution of Rare Eye Colors
While rare eye colors can pop up anywhere, there are certain parts of the world where they are slightly more common:
| Amber Eyes | Asia, South America |
| Red/Violet Eyes | Northern Europe |
| Heterochromia | Northern Europe |
| Black Eyes | Africa, Asia |
For example, amber eyes appear more frequently in Asian countries like India and Sri Lanka as well as parts of South America with indigenous populations. Red and violet eyes are most associated with people of Northern European descent, especially those with fair skin, light hair, and freckles. Conditions like heterochromia and aniridia seem to have higher rates among certain ethnic groups too. But these exotic eye colors can still appear anywhere.
Causes of Rare Eye Colors
So why do some people end up with such unusual eye colors? Here are some of the main causes:
Genetic Mutation
Many rare eye colors can be traced to genetic mutations that limit, alter, or reduce melanin pigment in the eyes. The exact genes involved are still being researched. But it seems that versions of genes like OCA2, HERC2, and SLC24A4 can delete melanin and create amber, red, and other light eye colors.
Low Melanin
Even without a specific genetic mutation, some eyes end up with very low amounts of melanin from birth. Since melanin produces brown pigment, low melanin can lead to light yellow, gold, red, or gray eyes depending on other factors.
Thinning of Iris
As we age, the iris can gradually thin and the muscle weakens. This allows more light to pass through and can produce eye colors that seem more vividly red, violet, or amber later in life. Aniridia is the extreme version, where the iris is completely missing at birth.
Lack of Pigment Cells
The complete lack of melanocytes, or melanin-producing pigment cells, can result in eyes with no color at all, known as ocular albinism. This creates a very light blue appearance that looks almost pink or violet.
Chimerism
Chimerism is a rare genetic condition where a person absorbs their twin’s cells in the womb. This can lead to eyes with two different colors – also called mosaic eyes – if the twins had different genetic eye colors.
Age and Eye Color
While your eye color is mostly determined at birth by your genes, some subtle changes can occur with age:
– Infants often have lighter blue eyes that can darken over the first year of life as melanin content increases.
– Hazel eyes may shift in balance of brown versus green.
– Eyes can seem darker with the development of limbal rings around the iris.
– Aging and the thinning of the iris muscle can cause some lightening of eye color later in life.
– Trauma, disease, and medications may also affect melanin and cause small changes in eye color.
But in general, the eye color you are born with will remain fairly stable barring these factors.
Conclusion
So in summary, the rarest eye colors in humans seem to be amber, red/violet, heterochromia, and black/aniridia eyes. Each of these exotic eye colors occurs in less than 1% of the global population. The cause is usually a genetic mutation or lack of melanin pigment. While these special eye colors are mostly determined at birth, there can be some natural variance with age. But no matter what shade your eyes are, they play an important role in vision and are a unique part of your appearance.