They are one of the first things we notice about someone.
But if you’re a sucker for big blue eyes, then you might be in for a shock – because according to science, they’re not blue at all.
Experts have discovered that the blue hue of the iris does not come from pigment, but from the scattering of light.
This phenomenon, known as the Tyndall effect, is repeated in the way that both the sky and the sea appear blue but are actually clear.
Dr Davinia Beaver from Bond University in Australia explained that the culprit is melanin, a substance in the body responsible for the color of our skin and hair.
“Brown eyes contain a high concentration of melanin, which absorbs light and makes them appear darker,” she wrote in Conversation . “Blue eyes contain very little melanin.”
‘In blue eyes, shorter wavelengths of light, such as blue, are scattered more efficiently than longer wavelengths, such as red or yellow.’
“Low melanin concentration results in less light being absorbed, allowing scattered blue light to dominate what we perceive. This blue hue results not from pigment, but from how light interacts with the structure of the eye.”
Experts have discovered that the blue hue of the iris does not come from pigment, but from light scattering (stock image)
On the other hand, green eyes are rare because they are the result of a genetic mutation that lowers melanin levels, but not as low as in blue eyes.
Hazel eyes are even more complicated – because the uneven distribution of melanin in the iris creates a “mosaic” of color that can change depending on the light.
Despite the decades-long assumption that eye color is controlled by a single gene, experts have recently learned that many genes determine this trait.
“This explains why children from the same family can have dramatically different eye colors and why two blue parents can sometimes have a child with green or even light brown eyes,” said Dr. Beaver.
To explain why many babies – especially those with European ancestry – are born with blue or gray eyes, Dr. Beaver said melanin levels are still low at this age.
As pigment gradually builds up over the years of life, these blue eyes can transition to green or brown.
In adulthood, eye color tends to be more stable, but it can be slightly affected by the light or even the shade of the clothes you wear.
Permanent changes are rare, but can occur as people age or in response to certain medical conditions.
Musician David Bowie’s eyes appeared different colors after an accident due to a permanently dilated pupil
Some celebrities, including Kate Bosworth and Mila Kunis, have a rare condition called heterochromia, where one eye is a different color to the other.
It can be genetic, the result of trauma, or related to specific health conditions, Dr. Beaver explained.
Musician David Bowie’s eyes appeared different colors after an accident due to a permanently dilated pupil, creating the illusion of heterochromia.
Blue is now the most common eye colour in Britain, figures show, while brown eyes are the most common eye colour in the world.
