Many newborns have eyes that are a pale blue or slate gray. This common phenomenon, particularly among infants of non-African or non-Asian descent, is not a guarantee of the final adult shade. The development of eye color is a gradual biological process driven by light exposure and a complex genetic blueprint. Observing this change is one of the memorable milestones of early childhood.
Why Many Newborns Have Grey or Blue Eyes
The initial pale hue seen in many babies’ irises is directly related to the amount of pigment present at birth. Eye color depends on melanin, the same pigment that colors skin and hair, which is produced by specialized cells called melanocytes located in the iris. At birth, these melanocytes have not yet been activated by light exposure, resulting in very little melanin deposited in the front layer of the iris, known as the stroma.
Without significant pigment, the iris tissue is largely transparent, and the eye appears blue or gray due to an optical effect. This effect is called Rayleigh or Tyndall scattering, where the collagen fibers in the stroma scatter shorter, blue wavelengths of light back out. As the baby is exposed to light, the melanocytes begin to increase melanin production, which starts the process of color deepening.
The Timeline for Eye Color Stabilization
The initial change in eye color often begins subtly during the first few months of life. Parents may notice the first visible shifts, such as flecks of green or brown appearing in the iris, around three to six months of age. A more noticeable progression usually occurs between six and nine months as pigment accumulates.
By a child’s first birthday, the eye color will likely have developed much of its permanent shade, providing a good indication of the final result. However, the process of pigment deposition is gradual and can continue beyond infancy. Eye color is generally considered stable by the age of three, although minor, subtle changes may continue throughout early childhood. The final color is a direct reflection of the genetically determined level of melanin that the melanocytes ultimately produce and store.
How Genetics Determines the Final Color
The ultimate eye color a baby develops is determined by a complex interplay of multiple genes, making it a polygenic trait. This inheritance pattern is far more intricate than the simple dominant/recessive model. Researchers have identified many genes that influence eye color, but two on chromosome 15, OCA2 and HERC2, are considered the most significant.
The OCA2 gene provides instructions for producing the P protein, which plays a role in the maturation of melanosomes, the structures that store melanin. Variations in this gene can reduce the amount of melanin produced, leading to lighter eye colors like blue or green. The HERC2 gene acts as a regulatory switch for OCA2, controlling whether the gene is turned on or off. A specific variation in HERC2 can reduce OCA2 activity, resulting in the minimal melanin needed for blue eyes.
Because multiple genes contribute, two parents with the same eye color can still have a child with a different shade. Even though brown eyes result from high melanin and are the most common color globally, two brown-eyed parents can carry variants for lighter colors that combine to produce a blue-eyed child. The final outcome is a unique combination of genetic instructions passed down, dictating the exact amount and type of melanin deposited in the iris.
When to Consult a Pediatrician
While eye color changes are a normal part of development, certain signs warrant immediate consultation with a healthcare provider. Parents should contact their pediatrician if they observe:
- Extreme asymmetry, where the two eyes develop completely different colors (heterochromia), especially if it appears suddenly.
- Any cloudiness, persistent redness, or a white or grayish-white color visible in the pupil.
- If the baby’s eyes do not seem to align or focus together after four months of age, or if they flutter quickly from side to side.