The Science of Infant Eye Color Development
The color of a baby’s eyes is determined by melanin, a pigment also responsible for skin and hair color. At birth, the specialized cells called melanocytes, which produce melanin, may not have fully developed or begun producing significant amounts of pigment. This initial lack of melanin means many newborns, particularly those with lighter skin tones, often present with blue or grey eyes.
The appearance of blue or grey eyes in infants is often due to a phenomenon known as Rayleigh scattering. When there is very little melanin in the front layers of the iris, light entering the eye is scattered, and shorter blue wavelengths are reflected more prominently. This scattering creates the illusion of blue or grey, similar to how the sky appears blue. Eyes with slightly more melanin may appear green or hazel due to the interaction of light with the light brown pigment.
As babies grow, their melanocytes begin to produce more melanin, leading to a gradual darkening or change in eye color. The ultimate amount of melanin produced is influenced by an individual’s genetic makeup. Genes dictate how much melanin is produced, transported, and stored within the iris. This genetic programming sets the stage for the eventual eye color.
When Baby Eye Color Stabilizes
Most eye color changes occur within the first six to twelve months of a baby’s life, with a more settled hue often evident by around nine months. This process is often stimulated by exposure to natural light, which encourages further melanin synthesis within the eye. However, the eye color can continue to refine and subtle shifts may occur for an extended period. In some instances, the permanent eye color may not fully emerge until a child is between three and six years old.
The progression of eye color typically moves from lighter shades to darker ones, meaning blue or grey eyes might transition to green, hazel, or brown as more melanin is deposited. Conversely, eyes that are already dark brown at birth are highly likely to remain brown and are less prone to significant lightening.
The Spectrum of Baby Eye Colors
Babies can be born with a range of initial eye colors, including brown, blue, or grey. A significant number of newborns, particularly those with darker complexions, are born with brown eyes. Research indicates that brown is the most common initial eye color, with nearly two-thirds of newborns observed having this hue.
For babies born with lighter eyes, such as blue or grey, these colors may evolve over time as melanin production increases. These initial lighter shades can transition to various final colors, including different shades of blue, green, hazel, or brown. The ultimate color that emerges depends on the genetically determined amount of melanin that accumulates in the iris over months and years.
Brown eyes are the most prevalent eye color globally and are the least likely to undergo a change from birth. If a baby is born with dark brown eyes, there is a high probability that their eyes will remain that color throughout their life, reflecting an already well-established melanin presence.