Blue eyes can turn hazel. This transformation typically occurs through natural developmental processes during early life or, less commonly, due to other factors later on.
The Science Behind Eye Color
Eye color is primarily determined by the amount and type of melanin present in the iris, specifically within its front layer called the stroma. There are two main types of melanin that influence eye color: eumelanin, which produces brown and black pigments, and pheomelanin, which contributes to red and yellow hues. The concentration of these pigments in the stroma dictates the perceived color of the eyes.
Blue eyes, for instance, contain very little melanin in the stroma. Instead of being a true blue pigment, the blue appearance results from the scattering of light within the stroma, a phenomenon known as Rayleigh scattering. This process causes shorter, blue wavelengths of light to be reflected, while longer wavelengths are absorbed. Eyes with slightly more melanin may appear green, while those with higher concentrations of eumelanin will appear brown.
Genetics play a significant role in determining the amount and type of melanin produced in the iris. Multiple genes interact to influence eye color, leading to the wide spectrum of colors observed across individuals. However, the expression of these genes and the subsequent melanin production can evolve over time, leading to shifts in eye color.
Natural Eye Color Changes
Many infants are born with blue eyes because their melanin production is not yet fully developed at birth. The melanocytes, the cells responsible for producing melanin, are still maturing and have not deposited their full pigment in the iris.
As a baby grows, typically during the first six months to three years of life, the melanocytes begin to produce and deposit more melanin in the iris. This increase in pigment can cause the eyes to darken. For some individuals, this natural accumulation of melanin can lead to a shift from blue eyes to green, hazel, or even brown.
This natural change from blue to hazel is a common developmental process, reflecting the ongoing maturation of the eye’s pigment-producing cells. These developmental changes are a normal part of human growth and do not indicate any underlying health concerns.
Other Influences on Eye Color
While natural development accounts for most eye color changes, other factors can also influence eye color, particularly in adolescence or adulthood. Certain medical conditions, though rare, can lead to shifts in eye color. For instance, heterochromia is a condition where a person has different colored eyes or different colors within one iris. This can be present from birth or develop later in life.
Fuch’s heterochromic iridocyclitis is another condition that can cause one eye to lighten or darken. Horner’s syndrome, which affects nerve pathways to the eye and face, can also result in a lighter eye color on the affected side. Additionally, some medications, such as certain glaucoma eye drops, have been observed to cause permanent darkening of the iris.
Physical trauma to the eye can also lead to changes in eye color, either by damaging pigment cells or altering the iris structure. Beyond these true physiological changes, eye color can also appear to shift due to perceived influences. Lighting conditions, the color of clothing, an individual’s mood, and even pupil dilation can temporarily alter how eye color is perceived. However, these are optical illusions and do not represent actual changes in the pigment content of the iris.