Gazing into a newborn’s eyes often sparks the question of what their permanent color will be. Many babies are born with a lighter eye color, typically blue or gray, which may not be their final hue. This initial color is a temporary placeholder because the eyes have not yet been exposed to light in the womb. The gradual shift parents observe is a predictable biological process that unfolds over the first few years of life.
The Role of Melanin in Infant Eye Color
The color of the iris, the ring of muscle tissue surrounding the pupil, is determined by a pigment called melanin. Specialized cells within the iris, known as melanocytes, are responsible for producing and storing this pigment. Melanin is the same substance that determines the color of a person’s hair and skin.
In the low-light environment of the womb, the melanocytes in a baby’s eyes are not yet fully active. At birth, a low concentration of melanin in the front layer of the iris causes light to scatter and reflect back, resulting in blue or gray eyes. Once exposed to natural light, the melanocytes begin to increase melanin production. This gradual accumulation of pigment causes the eye color to deepen and transition toward its final shade. The more melanin deposited, the darker the eye color will be; brown eyes have high levels of pigment, while blue eyes have minimal pigment.
The Timeline: When Eye Color Stabilizes
The eye color change typically becomes noticeable during the first six months of life. This is when melanocytes rapidly increase melanin production in response to light exposure. Parents might observe the initial blue or gray eyes starting to develop flecks of green, hazel, or brown as pigment is deposited.
By the time a baby reaches their first birthday, the eye color is usually close to its permanent state. The most significant changes occur between six and twelve months. However, fine changes can continue until the child is about three years old. In rare cases, slight color shifts, particularly in lighter shades, may be observed until the age of six.
How Genetics Determine the Final Hue
The ultimate shade of a baby’s eyes is determined by genetic material inherited from both parents. Eye color is a polygenic trait, meaning multiple genes interact to produce the final color, rather than being determined by a single gene. The two most significant genes involved are OCA2 and HERC2, located on chromosome 15, which primarily control the production and distribution of melanin.
Higher melanin production, which results in brown eyes, is associated with a dominant genetic influence. Conversely, lower melanin production, resulting in blue or green eyes, is associated with recessive genetic factors. If both parents have blue eyes, their child is highly likely to also have blue eyes. However, because multiple genes are involved, two parents with brown eyes may still carry the genetic code for lighter eye colors, making it possible to have a child with blue or green eyes.
Variations and When to Consult a Pediatrician
While the gradual change in eye color is a normal developmental process, certain variations should prompt a discussion with a healthcare provider. Heterochromia is a condition where a person has different-colored eyes, or different colors within the same iris. This variation is often a benign genetic trait that causes no vision or health problems.
However, congenital heterochromia can sometimes be associated with underlying health issues, such as Waardenburg syndrome or Horner’s syndrome. A sudden or dramatic change in eye color in one eye after infancy, or the appearance of a dark spot on the iris, may signal an acquired condition, such as injury or inflammation. In these instances, the child should be examined by a pediatric ophthalmologist to rule out rare medical causes.