When a new baby arrives, the color of a newborn’s eyes is a common source of curiosity, as the initial shade often does not last. Changing eye color is a normal and expected part of an infant’s development. While genetics set the stage for the ultimate outcome, the final color takes time to reveal itself fully. This subtle biological process unfolds across the first few years of life.
The Typical Timeline for Eye Color Change
The eye color seen at birth is typically a temporary shade, often blue or gray, especially for infants of lighter-skinned heritage. This initial hue is not a guarantee of the final color. Noticeable shifts usually begin around three to six months of age as the infant is increasingly exposed to light.
The period between six and nine months is when the most significant change becomes apparent. The iris may start to show flecks of a different pigment, such as brown, hazel, or green, as the color deepens or changes completely. Many babies will have a color close to their final shade by their first birthday, but the process is not always complete.
Eye color commonly continues developing throughout the toddler years. Experts consider the color to be relatively stable and permanent sometime between one and three years old. Any sudden change beyond the toddler years should be discussed with a doctor.
The Role of Melanin in Iris Color
Eye color is determined by the amount of melanin pigment contained within specialized cells called melanocytes in the iris. Melanin also influences the color of a person’s hair and skin. Eyes with a large amount of melanin appear brown, while eyes with very little melanin appear blue due to how light scatters through the iris tissue.
Babies are often born with lighter eyes because melanocytes have not yet begun producing substantial melanin. Inside the womb, the pigment cells are not fully activated. Exposure to natural light after birth stimulates the melanocytes to begin producing and depositing more melanin into the iris.
The color change is the gradual process of this pigment production increasing over time. If melanocytes produce a small amount of melanin, the eyes will likely remain blue or turn green. If the cells produce a significant amount, the eyes will transition to a darker color like brown.
Genetic Inheritance of Eye Color
The final eye color a baby develops is dictated by the genes inherited from both parents. Eye color inheritance is a complex trait involving multiple genes, including OCA2 and HERC2 on chromosome 15. The interaction of these genes controls the amount and distribution of melanin in the iris.
Because of this polygenic inheritance, the old model of simple dominant and recessive genes (where brown always dominates blue) is overly simplistic. Parental eye colors offer a strong clue but do not guarantee the child’s final shade. For example, two brown-eyed parents can still have a blue-eyed child if they both carry the genes for lighter eye colors.
Generally, if both parents have blue eyes, the baby has a very high probability of having blue eyes. Similarly, if both parents have brown eyes, the child is most likely to have brown eyes. However, the complexity of multiple genes means that unexpected combinations are possible.