Why Are Babies Born with Blue Eyes?

Understanding Melanin and Eye Color

It takes a while before melanin is deposited fully in human eyes, so babies often have pale or blue eyes, even though their eyes may change color later in life.
It takes a while before melanin is deposited fully in human eyes, so babies often have pale or blue eyes, even though their eyes may change color later in life. Daniel MacDonald / www.dmacphoto.com / Getty Images

You may have heard it said that all babies are born with blue eyes. You inherit your eye color from your parents, but no matter what the color is now, it may have been blue when you were born. Why? Melanin, the brown pigment molecule that colors your skin, hair, and eyes, hadn't been fully deposited in the irises of your eyes or darkened by exposure to ultraviolet light. The iris is the colored part of the eye that controls the amount of light that is allowed to enter.

Like hair and skin, it contains the pigment, possibly to help protect the eye from the sun.

How Melanin Affects Eye Color

Melanin is a protein. Like other proteins, the amount and type you get is coded in your genes. Irises containing a large amount of melanin appear black or brown. Less melanin produces green, gray, or light brown eyes. If your eyes contain very small amounts of melanin, they will appear blue or light gray. People with albinism have no melanin in their irises and their eyes may appear pink because the blood vessels in the back of their eyes reflect light.

Melanin production generally increases during the first year of a baby's life, leading to a deepening of eye color. The color is often stable by about 6 months of age, but it may take as long as two years to develop. However, several factors can affect eye color, including use of certain medications and environmental factors.

Some people experience changes in eye color over the course of their lives. People can have eyes of two colors. Even the genetics of eye color inheritance isn't as cut-and-dried as was once thought, as blue-eyed parents have been known (rarely) to have a brown-eyed child!

Also, not all babies are born with blue eyes.

A baby may start out with gray eyes, even if they ultimately become blue. Babies of African, Asian, and Hispanic descent are more likely to be born with brown eyes. This is because darker-skinned individuals tend to have more melanin in their eyes than Caucasians. Even so, a baby's eye color may deepen over time. Also, blue eyes are still possible for babies of dark-skinned parents. This is more common in preterm babies, because melanin deposition takes time. 

Eye Color Fun Facts: Humans aren't the only animals that experience eye color changes. For example, kittens are often born with blue eyes, too. In cats, the initial eye color change is fairly dramatic because they develop so much more quickly than humans. Feline eye color changes over time even in adult cats, generally stabilizing after a couple of years.

Even more interesting, sometimes eye color changes with the seasons! For example, scientists have learned reindeer eye color changes in the winter. This is so reindeer can see better in the dark. It's not only their eye color that changes, either. The collagen fibers in the eye change their spacing in the winter to keep the pupil more dilated to capture as much light as possible.