Before answering that it is due to being fed exclusively on mother’s milk, we can already say that this is not the right answer. Most babies are born with grey eyes for another reason that is much more complex and curious…

Actually, it can be said that the great majority of babies are born with grey eyes, or an undefined colour. And this undefined colour remains for the first few months. This phenomenon is due to nothing more and nothing less than a protein, or in this case, the lack of it!

It turns out that the colour of the iris, like the pigmentation of the skin, depends on a protein known as melanin. Melanin is a type of protein produced by cells specialised for this function which are called melanocytes. Thus, these cells are responsible for the secretion of melanin. This protein is responsible not only for pigmentation of the skin, eyes and hair of human beings, but also for protecting the DNA of cells against ultraviolet radiation emitted by the sun.

When a baby is born, the melanocytes are still immature. However, as these cells mature, they start to produce melanin. Consequently, the baby’s eye colour is gradually defined.

Before answering that it is due to being fed exclusively on mother's milk, we can already say that this is not the right answer. Most babies are born with grey eyes for another reason that is much more complex and curious...
CREDIT: BIBEK THAKURI / UNSPLASH

In short, most babies are born with grey eyes, which in reality is an undefined colour. The colour of the iris begins to define itself as the melanocytes secrete melanin. Therefore, a baby does not change the colour of its eyes from grey to brown or green. What does happen is a process in which the baby’s eye colour gradually defines itself. This process can last from 6 to 12 months.

And what defines the definitive colour of the eyes?

The definitive colour of a baby’s eyes depends on the quantity of melanin secreted. Therefore from the age of six months the definition of the colour begins. The quantity of melanin secreted will influence the definitive colour in the following way:

  • Blue: when a reduced amount of melanin is secreted.
  • Green or honey-coloured: when a slightly greater amount is secreted.
  • Brown to very dark brown: when a substantial amount of melanin is secreted; this is therefore the most common eye colour.

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