Many babies are born with blue or grey eyes, a color that often changes as they grow. This shift is a normal biological process.
What Gives Eyes Their Color?
Eye color originates primarily from melanin, a pigment also responsible for skin and hair color. Specialized cells called melanocytes produce melanin within the iris, the colored part of the eye. The amount and distribution of this melanin determine the specific hue of the eyes. High concentrations of melanin result in brown eyes, which are the most common eye color globally.
Eyes with intermediate melanin levels can appear green, hazel, or amber. In contrast, blue eyes have very low melanin content in the iris. The appearance of blue eyes is not due to a blue pigment, but rather to the scattering of light in the iris’s stroma, a connective tissue layer. This phenomenon, similar to how the sky appears blue, is known as Rayleigh scattering, where shorter blue wavelengths of light are reflected more than longer ones.
How Babies’ Eyes Change Color
Babies are born with blue or grey eyes because their irises contain little to no melanin at birth. This initial lack of pigment results from limited light exposure inside the womb, meaning melanocytes, the melanin-producing cells, haven’t been stimulated to produce significant pigment. After birth, as a baby’s eyes are exposed to light, these melanocytes activate and begin producing melanin.
As melanin production increases and pigment accumulates in the iris, eye color gradually darkens or shifts. For instance, initially blue eyes may transition to green, hazel, or brown as more melanin is produced. The amount of melanin produced influences the final eye color.
When Eye Color Stabilizes
The most significant changes in a baby’s eye color typically occur within the first six to twelve months of life. While many infants’ eye colors stabilize around their first birthday, minor changes can continue for a longer duration.
Eye color can continue to subtly change up to three years of age, or even later. Not all babies experience a dramatic color change; for example, babies born with brown eyes typically have sufficient melanin from birth, so their eye color is less likely to change significantly.
The Role of Genetics in Eye Color
While the change in eye color after birth is influenced by melanin production, genetics ultimately determine the potential and final amount of melanin an individual’s melanocytes can produce. Eye color is a complex trait influenced by multiple genes inherited from both parents, rather than a single gene.
Genes such as OCA2 and HERC2, located on chromosome 15, play a major role in controlling the amount and quality of melanin in the iris. These genes influence the likelihood of specific eye colors, with brown eyes generally being a more common trait due to higher melanin levels. Although it was once thought that brown eyes were strictly dominant over blue eyes, the involvement of multiple genes means that eye color inheritance is more intricate. This genetic predisposition guides the melanin development process, ultimately determining the baby’s permanent eye color.