Many new parents observe that their baby’s eyes are a striking shade of blue or gray shortly after birth. For many infants, this initial shade is only temporary, representing a stage in the eye’s development. The final eye color is a gradual process determined by genetics and time, unfolding over the first few years of life.
The Science Behind Initial Eye Color
The appearance of blue or gray eyes in a newborn is primarily due to a temporary lack of pigment in the front layer of the iris. Melanin, which colors skin and hair, determines the final eye color. However, at birth, the specialized pigment-producing cells, called melanocytes, have not yet fully activated in the iris.
The initial light color is an optical effect, not the result of blue pigment being present. When light enters the iris, the low concentration of melanin in the stroma causes the light to scatter. This phenomenon, known as Rayleigh scattering, preferentially disperses shorter, blue wavelengths of light, making the eyes appear blue or gray, much like the sky.
Melanocytes begin producing and depositing melanin into the iris only after the baby is exposed to light. The amount of melanin produced over time determines whether the eyes remain blue or shift to green, hazel, or brown. Babies with darker skin tones often have a higher baseline of melanin at birth, so their eyes may be born brown or dark gray and experience little change.
The Typical Timeline of Eye Color Change
The process of eye color change begins once melanocytes are stimulated by light exposure. The most significant color shifts typically occur within the first six to nine months of life.
Parents often see a definite change between three and six months as melanocytes become more active and start producing melanin. The color may deepen or take on new shades, transitioning from a light blue to a grayish-green or a warmer brown.
By the time a child reaches their first birthday, the eye color is usually close to its permanent shade, as the majority of melanin production has taken place. For most children, the color is considered stable by 12 to 18 months of age. Subtle changes, particularly a shift toward a darker shade, can continue until the child is about three years old.
Genetics: What Determines the Final Shade
The final eye color is determined by inherited instructions for how much melanin the melanocytes will produce. This is a complex trait influenced by multiple genes, not just a single “eye color gene.”
Researchers have identified several genes, including OCA2 and HERC2, that control the amount and distribution of melanin in the iris. The combination of variants from both parents instructs the body on the total potential for pigment production.
Genes that code for high melanin production tend to result in brown eyes. Conversely, genes that result in low melanin production lead to lighter eye colors like blue. Because multiple genes are involved, two parents with brown eyes can still have a child with blue eyes, though this is less common.
When Eye Color Changes May Need Attention
While gradual eye color change is a normal part of infant development, certain patterns may warrant consultation with a pediatrician or pediatric ophthalmologist. One observation is heterochromia, a condition where a child has two different colored eyes, or a single eye has a patch of color different from the rest of the iris.
Though heterochromia is often a harmless genetic variation, it can rarely be associated with an underlying health condition, so a medical evaluation is prudent. Parents should also seek attention if they notice sudden changes in eye color after age three, or if the eye appears cloudy or has a white or pinkish reflection in the pupil.