It is a common belief that all babies are born with blue eyes. However, this is a widespread misconception. While many infants may indeed have blue or grayish eyes at birth, a significant number of newborns arrive with brown, green, or hazel eyes. The initial eye color observed in a baby is not necessarily their permanent shade, as it can undergo changes during the first few years of life.
Initial Eye Color: The Melanin Connection
A newborn’s initial eye color is primarily determined by the amount of melanin present in the iris, the colored part of the eye. Melanin is a pigment produced by specialized cells called melanocytes, which also contribute to skin and hair color. At birth, melanocytes in a baby’s iris may not have fully developed or begun producing melanin consistently due to the dark environment of the womb.
Consequently, eyes that appear blue or gray in infants often have very little melanin in the front layers of the iris. This appearance is largely due to a phenomenon known as Rayleigh scattering, where shorter blue wavelengths of light are scattered more effectively than other colors. As a result, the perceived color is blue, even though there is no blue pigment. Conversely, babies with more active melanocytes at birth frequently have brown eyes that contain a higher concentration of melanin.
The Genetics of Eye Color Development
The ultimate color of a person’s eyes is a complex trait influenced by multiple genes. Among the most significant genetic contributors are the OCA2 and HERC2 genes. The OCA2 gene provides instructions for making the P protein, which is integral to the production and storage of melanin within melanosomes in the iris.
The HERC2 gene acts as a regulatory switch for OCA2. A specific variant within the HERC2 gene can reduce the expression of OCA2, leading to decreased production of the P protein and, consequently, less melanin in the iris. This lower melanin concentration results in lighter eye colors, such as blue. Higher levels of melanin lead to brown eyes, while intermediate amounts can produce green or hazel shades. Other genes, including TYR and TYRP1, also play smaller roles by influencing the melanin production and transport pathways.
When Eye Color Becomes Permanent
A baby’s eye color is not fixed at birth and typically undergoes changes as melanin production increases following exposure to light. The most noticeable shifts in eye color usually occur within the first six to twelve months of life. During this period, melanocytes become more active, depositing additional melanin into the iris.
While many infants’ eye colors stabilize by approximately nine months to one year of age, subtle changes can continue for a longer duration. Eye color can continue to shift gradually until a child is around three years old, and in some instances, minor changes may even persist up to six years of age or into adolescence. Generally, any changes observed will involve the eyes darkening, for example, from blue to green, hazel, or brown, rather than becoming lighter.