The first glimpse into a newborn’s eyes often reveals an indistinct, light color, frequently a shade of slate blue or soft grey. This observation has led to the belief that all babies are born with blue eyes, though this is not strictly true. This light, temporary hue is a normal stage in human development, resulting from biological processes that are not yet complete at birth. The initial color is a snapshot of an eye preparing to settle on its final, genetically determined shade.
The Role of Melanin in Eye Color
The true color of the human eye is determined by melanin, a pigment also responsible for the color of skin and hair. Eye color is dictated by the amount and distribution of this pigment within the iris, the colored ring that surrounds the pupil. Specialized cells within the iris, known as melanocytes, produce and secrete melanin.
The concentration of melanin in the stroma, the front layer of the iris, determines the resulting eye color. High concentrations of melanin appear brown or black, which is the most common eye color worldwide. Very little melanin in the stroma results in blue eyes, while intermediate amounts result in shades like green or hazel. Genetic information inherited from both parents dictates the capacity of melanocytes to produce the pigment.
Why Eyes Appear Grey at Birth
The reason many newborns display a grey or light blue eye color is twofold: an immature biological system and a phenomenon of light physics. At birth, the melanocytes in the iris have not been fully activated, meaning they have not begun to deposit significant melanin into the iris stroma. Because the baby developed in the dark environment of the womb, the pigment-producing cells have not been stimulated by light.
This lack of pigment creates the conditions for an optical effect known as light scattering. Light entering the eye passes through the nearly transparent stroma, which contains fine collagen fibers. When light hits these fibers, longer, red and yellow wavelengths pass straight through, but shorter, blue wavelengths are scattered back toward the observer. This effect is similar to how the Earth’s atmosphere scatters sunlight, making the sky appear blue.
The resulting color is not a true reflection of blue pigment, but an illusion created by the stroma’s structure and the absence of melanin to absorb scattered wavelengths. This explains the indistinct, often slate-grey or light-blue appearance common in newborns, particularly those of lighter skin tones. Babies genetically predisposed for darker eyes, such as those of African, Asian, or Hispanic heritage, may be born with dark brown eyes because their melanocytes were active during gestation.
The Timeline of Eye Color Change
The initial grey or blue shade is temporary because melanocytes increase their activity once the eyes are regularly exposed to light after birth. This exposure acts as a stimulus, prompting the cells to start producing and depositing melanin into the iris stroma. As more pigment is produced, the eye color transitions toward the final, permanent color.
The most noticeable changes occur between three and six months of age. By the time a baby reaches their first birthday, the eye color has often stabilized enough to indicate the final shade. However, the process is not always complete, and subtle shifts can continue for a longer period.
In some cases, the eye color may continue to darken or change slightly until the child is two or even three years old. For a baby genetically programmed for brown eyes, the change from the initial light color is the most dramatic, as the melanocytes deposit a large amount of pigment. If the eye color is meant to remain blue, the melanocytes will deposit only a minimal amount, and the color will simply refine its initial shade.