In the first months of life, a newborn’s eyes often appear to shift in color. The light shade seen at birth, frequently blue or gray, is usually temporary and not the final adult color. This normal change results from biological processes as the infant adapts to life outside the womb. The eyes generally move toward a permanent shade, which is almost always a darkening of the initial color.
Biological Mechanism of Eye Color Change
The color of the iris is determined by the amount of the pigment melanin present. Specialized cells called melanocytes produce this melanin, the same substance that colors the skin and hair. Many newborns have low levels of melanin because melanocytes have not been activated by light exposure in the dark environment of the womb.
After birth, light exposure stimulates melanocytes to begin producing and depositing melanin into the iris. Increased melanin production leads to a darkening of the eyes over time. Large amounts of melanin result in brown eyes, while moderate amounts may result in green or hazel eyes. If melanocytes produce very little melanin, the eyes remain blue or gray due to the scattering of light by the iris tissue, not blue pigment.
Timeline for Final Eye Color
The most significant changes in eye color typically occur within the first year of life. The period between six and nine months often sees the most dramatic shift as melanin production ramps up. While the color is fairly stable by the time the baby reaches one year, subtle shifts can continue.
Eye color transition can continue until the child is around three years old. Babies born with dark brown eyes are likely to remain dark, though the specific shade may deepen slightly. For those born with a lighter shade, the first three years represent the typical window for the eyes to transition to their genetically determined final color.
What Determines a Baby’s Final Eye Color
The final eye color is fundamentally dictated by genetics, involving a complex interplay of multiple genes inherited from both parents. Eye color is a polygenic trait, controlled by more than two genes, with up to 16 genes potentially contributing to the final shade. Influential genes, such as OCA2 and HERC2, regulate the amount and type of melanin the melanocytes produce.
The combination of parental genes determines the range of melanin production the child will achieve. This genetic complexity explains why two parents with brown eyes can sometimes have a child with blue eyes, though this is less common. While dark eye colors are often more dominant, the final color results from specific gene variations passed down and expressed in the iris.
When Eye Color Changes Indicate a Problem
Gradual changes in eye color during infancy are a normal part of development and should not cause concern. However, rare instances exist where an eye color change can signal a medical issue, warranting a visit to an ophthalmologist. One sign is heterochromia, where the two eyes are distinctly different colors or one iris has multiple contrasting sections.
While heterochromia can be a harmless genetic condition, it can sometimes be associated with syndromes or trauma. A sudden, noticeable color change in only one eye or a change occurring after the age of three should be evaluated. In adults, changes like a darkening or lightening of one iris can be linked to conditions such as inflammation, injury, or specific disorders like Fuchs’ heterochromic iridocyclitis.