Eye color is a remarkable human characteristic, often among the first features noticed about an individual. Many new parents observe that their baby’s eye color, initially a lighter shade, frequently changes over the first few months of life. This natural phenomenon prompts curiosity about when a child’s definitive eye color will emerge.
How Eye Color Develops
Eye color results from the amount and type of melanin present within the iris, the colored part of the eye. Melanin is a pigment produced by specialized cells called melanocytes. Two main types of melanin contribute to eye color: eumelanin, which produces brown and black shades, and pheomelanin, which contributes to red and yellow tones.
The specific shade of a person’s eyes depends on the concentration and distribution of these pigments in the iris’s front layer, known as the stroma. For instance, a high concentration of eumelanin results in brown eyes. Lower amounts of eumelanin, combined with light scattering in the stroma, can create blue eyes, while intermediate levels might lead to green or hazel eyes. Genetic factors largely influence the amount and type of melanin that melanocytes produce.
The Timeline of Eye Color Stabilization
Most infants are born with eyes that appear blue or grayish because their melanocytes have not yet begun to produce significant amounts of melanin. As babies grow, their eyes are increasingly exposed to light, which stimulates the melanocytes in the iris to produce and accumulate more melanin.
This gradual increase in melanin production is what causes the observed changes in eye color. The most noticeable shifts occur within the first six to twelve months of life. While significant changes often stabilize by the first birthday, the process can continue until a child is approximately three years old. Once this period of increased melanin production and deposition concludes, the eye color is considered set and permanent.
Why Eye Color Can Still Change Later
While eye color is largely established in early childhood, certain rare circumstances can lead to subtle or even noticeable changes later in life. Medical conditions can alter eye color. For instance, Horner’s syndrome can cause one eye to become lighter, while Fuch’s heterochromic iridocyclitis can lead to one eye gradually changing color.
Some glaucoma drops can cause a darkening of the iris over time. Physical trauma to the eye can also disrupt melanin distribution, leading to a change in color. Additionally, subtle shifts in eye color can occur with advanced aging as melanin can degrade slightly, but these changes are not dramatic.