Barbara Marquand is a staff writer at NerdWallet, a personal finance website. Email: bmarquand@nerdwallet.com. Twitter: @barbaramarquand.
The eye may change color due to alteration of genes in the cells of the iris. This is because of your DNA factors in the body. The gene alteration can cause the eye to change color from brown to green and vise verse. There is no any explanation to the cause of the genes behaving in these manner. Prolonged exposure to the sun might also be another cause that made my eyes to change the color.
If your eyes check out fine, then the cause of the color change is probably due to age. Aging is the most common cause of a change in eye color, gradually, after reaching adolescence. Most will lighten with age, but hazel (light brown or yellowish brown) or blue can darken.