A baby’s eye color can change after birth, a common developmental process influenced by the gradual production of pigment in the eyes. Many newborns may have lighter eye colors, such as blue or gray, but these hues are not always permanent.
The Science of Eye Color
Eye color is determined by the amount and type of melanin in the iris, a pigment also responsible for skin and hair color. Two main types of melanin influence eye color: eumelanin (brown and black tones) and pheomelanin (amber, green, or hazel hues).
The concentration and distribution of these pigments determine the perceived color. For instance, brown eyes have a high concentration of eumelanin, absorbing most light. In contrast, blue eyes have very little melanin in the front layers of the iris; their blue appearance results from light scattering within the iris’s stroma, similar to how the sky appears blue. Green and hazel eyes contain intermediate amounts of melanin, with green eyes also involving light scattering combined with a yellowish pigment.
Why and When Eye Color Changes
A baby’s eye color changes because melanin production in the iris is not fully developed at birth. Melanocytes, the cells that produce melanin, continue to develop and become more active after birth. Exposure to light stimulates these melanocytes to produce more pigment, leading to a gradual shift in eye color, often resulting in darker eyes.
Most noticeable changes occur between 6 and 12 months of age. While many babies show their likely final eye color by their first birthday, subtle changes can continue until a child is around 3 years old, and sometimes up to 6 years for lighter eye colors. It is common for eyes to transition from lighter shades like blue or gray to green, hazel, or brown. However, eyes that are dark brown at birth are less likely to change significantly and typically remain brown.
Genetic Blueprint for Eye Color
Genetics play a significant role in determining eye color, influencing the amount and type of melanin produced. Eye color inheritance is a complex trait, meaning multiple genes contribute to the final outcome, rather than a simple dominant or recessive pattern. This is known as polygenic inheritance.
Two genes, OCA2 and HERC2, located on chromosome 15, are major contributors to eye color. The OCA2 gene is involved in the production of the P protein, which is essential for melanin synthesis. The HERC2 gene acts as a regulator, controlling the activity of the OCA2 gene. Variations in these genes can lead to different levels of melanin, influencing whether eyes are lighter or darker. While parental eye colors offer clues about a child’s potential eye color, the involvement of multiple genes means that predicting the exact shade can be challenging.