Newborns often have light-colored eyes, typically blue or gray, leading parents to wonder what their permanent eye color will be. The initial color frequently shifts as the baby grows. When a baby’s eye color settles is determined by biology, timing, and inherited genetic instructions influencing pigments and light.
How Melanin Determines Eye Color
Human eye color is determined by melanin, a brownish-black pigment housed within the iris. The amount of melanin present creates the color spectrum. High concentrations of melanin in the front layer of the iris absorb most light, resulting in darker colors like brown or black.
Eyes with very low amounts of melanin appear blue due to Rayleigh scattering, not blue pigment. This physical phenomenon causes shorter blue wavelengths of light to scatter and reflect, similar to how the sky appears blue. Green eyes contain slightly more melanin than blue eyes, while hazel or amber result from moderate amounts combined with light scattering. The final eye color reflects the activity of melanocytes, the cells that produce and store melanin within the iris.
The Typical Timeline for Color Stabilization
Many babies are born with light eyes because melanocytes in the iris have not yet produced their full, genetically determined amount of melanin. Since production is minimal before birth, blue or gray is the default initial color for many infants. Once exposed to light after birth, melanocytes increase melanin production, starting the process of color change.
The most noticeable and dramatic shifts in eye color typically occur within the first six to nine months as melanin is continually deposited into the iris. During this period, a light blue or gray can gradually deepen into green, hazel, or brown as the pigment concentration increases. For many babies, the eye color settles into a more permanent hue by the time they reach their first birthday.
However, the process is not always complete within the first year, and subtle color changes can continue longer. While the color is largely established by 12 months, minor shifts may still be observed until a child is about three years old. This extended timeline is common for lighter colors like green or hazel, which depend on a precise, moderate amount of melanin. Once eyes transition to dark brown, that color is highly likely to remain permanent.
Predicting Eye Color Through Genetics
Eye color inheritance is a polygenic trait, meaning multiple genes influence the final shade, making it more complex than the simple dominant and recessive model. While brown eyes are generally considered dominant and blue eyes recessive, the interaction of at least eight different genes makes predicting the exact color challenging. The OCA2 and HERC2 genes, located on chromosome 15, are primary genetic factors regulating melanin production in the iris.
The overall genetic code dictates the maximum amount of melanin melanocytes can produce, setting the range for the final eye color. Despite the complexity, parents can look to their own and extended family’s eye colors for an estimated probability. For instance, two parents with brown eyes have a high probability of having a brown-eyed child, but a blue-eyed child remains possible if both carry the genetic information for blue eyes.
The full range of possibilities, including colors like green or hazel, is determined by the specific combination of alleles inherited from both parents. Because multiple genes are involved, a child can sometimes have an eye color that is not immediately obvious from looking at the parents.