In addition to the color of a baby's eyes, melanin is responsible for determining hair and skin color. When a baby is born, his or her body starts producing melanin, which is secreted by special cells called melanocytes. The more melanin that melanocytes secrete, the darker a baby's eyes will be. If melanocytes only secrete a small amount of melanin, a baby's eyes will remain a light color such as blue or hazel. A baby whose melanocytes secrete higher levels of melanin will end up with darker eyes such as brown. Regardless of how much melanin secreted, melanocytes are most active during the first nine months of a baby's life, which is why the eyes change color most rapidly during that time. Because eye color is encoded in a baby's genes, it cannot be changed by external factors. Parents, for instance, cannot make their baby's eyes turn lighter or darker by controlling his or her exposure to light. Although diet can help with a baby's eye health, the foods that he or she eats do not influence eye color either.
Genes are the ultimate determinant of eye color, and determining eye color can be complicated. The likelihood that a child will end up with eyes of a certain color is influenced largely by the parents' eye colors, but eye color can also be determined through recessive genes. If both parents have brown eyes, for example, there is a high probability their child will also have brown eyes. But if there is genetic coding in either parent's lineage for green or blue eyes, those genes can be passed along to the child and he or she can have lighter eyes. If one brown-eyed parent's mother or father has blue eyes, the chances are slightly higher that a baby will also have blue eyes. If one parent has brown eyes and the other has blue eyes, there is about a 50-50 chance of the baby ending up with either one of those eye colors.
Eye color change is normal in babies, but parents should watch for other signs of abnormalities and eye problems. Parents should bring their children to a pediatrician if they notice that only one eye changes color, which can indicate a genetic problem. A child with one brown eye and one blue eye, for instance, may have Waardenburg syndrome, which is a rare genetic disorder. Eye cloudiness is also abnormal and warrants a professional evaluation.