The appearance of a newborn’s eyes is often one of the first features parents observe; many babies are born with eyes that appear blue or grayish. This initial shade frequently sparks curiosity about what the permanent color will be. The final eye color is not present at birth because it depends entirely on the amount of pigment that develops in the iris over time. The lasting hue of the eyes is determined by the complex interaction of genetics and the physical presence of pigment.
How Melanin Determines Eye Color
The color of the iris is directly proportional to the concentration of a pigment called melanin. Melanin is produced by specialized cells within the iris, known as melanocytes, and is the same substance responsible for coloring hair and skin. Many infants are born with lighter eyes because melanocyte activity is low or dormant in the womb, resulting in a lack of color.
Once a baby is exposed to light after birth, the melanocytes become activated and begin to produce melanin. If only a small amount of melanin is deposited, the eyes will appear blue because of the way light scatters through the tissue. Increased melanin production leads to darker colors; a moderate amount results in green or hazel, while a high concentration results in brown eyes. The more active the melanocytes, the darker the final eye color will be.
The Typical Timeline for Color Change
The most significant changes in a baby’s eye color occur during the first year of life as the melanocytes react to light exposure. Subtle shifts may begin as early as three months, when parents might notice the first flecks of a new color appearing in the iris. The change becomes more noticeable between six and nine months of age, with the color often deepening as melanin production accelerates.
By the time a baby reaches their first birthday, the eye color is usually close to its permanent shade. The American Academy of Ophthalmology suggests that most children have their lifelong eye color by about nine months old. However, subtle changes can continue beyond this stage.
For some children, the final stabilization of eye color may not happen until they are two or three years old. These changes are often minor refinements, such as a shift from a blue-green to a hazel, rather than a dramatic transformation. Although minor color alterations can continue up to the age of six in rare cases, the color is generally considered permanent by the toddler years.
Understanding Genetic Influence
The final eye color a child develops is determined by a complex system of genetic inheritance. Eye color is considered a polygenic trait, meaning multiple genes interact to determine the final outcome, rather than being controlled by a single gene. Scientists have identified at least eight genes that influence the color, with the OCA2 and HERC2 genes playing the most significant roles in the blue-brown color spectrum.
The OCA2 gene controls the production of the P-protein, which is involved in melanin formation. Variations in the HERC2 gene can affect how much OCA2 is expressed, regulating the overall amount of melanin produced in the iris. Since darker colors are associated with higher melanin levels, brown eyes are generally considered a dominant trait, while blue eyes, which have the least pigment, are typically recessive.
This polygenic model explains why two parents with brown eyes can still have a child with blue eyes, especially if lighter eye colors exist in the grandparents’ generation. The combination of multiple genes dictates the potential range of melanin production. The genetic code sets the ceiling for how much pigment the melanocytes can produce, which ultimately settles the permanent eye color.