Observing a newborn’s eyes often reveals a surprising shade of grey or blue, leading many parents to wonder about their child’s future appearance. This initial light color is a normal physiological stage of development, not necessarily indicating the final adult eye color. The color of the iris, the muscular ring surrounding the pupil, is determined by a complex interplay of biology and genetics. The transformation from that first light shade to a permanent hue is an expected part of infant growth.
The Reason Babies Are Born With Light Eyes
The appearance of a grey or light blue shade in a newborn’s eyes is due to the lack of pigment in the front layer of the iris. Eye color is determined by melanin, the protein that colors skin and hair, and the amount present in the iris’s stroma layer. At birth, the specialized cells responsible for producing melanin, called melanocytes, have not yet been fully activated by light exposure.
Because little to no melanin has been produced, the stroma is relatively colorless. The blue or grey appearance is an optical illusion caused by the physics of light scattering. When light enters the iris, the shorter blue wavelengths are reflected back out, a phenomenon known as Tyndall scattering. This effect is similar to what makes the sky appear blue and gives the eyes their initial light coloration. As the eyes are exposed to light, the melanocytes begin to produce pigment, initiating the color change process.
The Typical Timeline for Eye Color Change
The process of eye color darkening begins as soon as the melanocytes start producing melanin. Changes may first become noticeable around three to six months of age as flecks of color like green, hazel, or brown begin to appear. The most significant period of change typically occurs between six and twelve months of age, when the color becomes much more settled.
By the time a child reaches their first birthday, their eye color is usually very close to its final adult shade. However, the process is not always complete at one year, especially for children who end up with lighter colors like blue or green. Subtle changes may continue until a child is around three years old, and in rare cases, even up to six years of age. If the eyes are dark brown at birth, the color is highly unlikely to change to a lighter shade over time.
How Genetics Determine the Final Color
The final eye color is a complex, polygenic trait determined by the interaction of multiple genes inherited from both parents. Scientists have identified up to 16 different genes that influence eye color, but two major genes, OCA2 and HERC2, play the primary role. The OCA2 gene, located on chromosome 15, provides instructions for creating a protein involved in melanin production.
The nearby HERC2 gene acts like a control switch, regulating how much of the OCA2 gene is expressed, which controls the amount of pigment made. A specific variation in the HERC2 gene can reduce the expression of OCA2, leading to less melanin and resulting in blue eyes. This complex interaction explains why the old model—which suggested brown eyes are simply dominant over blue eyes—is inaccurate. For instance, two parents with brown eyes can still have a child with blue eyes because of the combination of genetic variations they pass on.
Signs That Warrant a Doctor’s Visit
While eye color changing is normal, certain signs related to eye appearance or function should prompt a visit to a pediatrician or pediatric ophthalmologist. If one iris is a noticeably different color than the other, a condition called heterochromia, it should be evaluated. This condition is often harmless but can occasionally be associated with certain syndromes or underlying issues.
Any sudden change in eye color after the first few years of life warrants medical attention. Parents should also watch for concerning signs, including:
- Abnormal cloudiness or a white or yellow material in the pupil.
- A lack of the “red reflex” when a picture is taken with a flash.
- Persistent tearing, redness that does not resolve, or pus.
- An eye that appears to wander or is misaligned after six months of age.