Why Do We Have Different Eye Colours? The Science Behind It

Written by Karan Sharma

Eye colour is one of the most striking human features, shaped by light, pigment and genetics.

[{"selector":"#anim-01808186-ce08-444c-adaa-995fb4755062","keyframes":{"opacity":[0,1]},"delay":250,"duration":2000,"easing":"cubic-bezier(0.4, 0.4, 0.0, 1)","fill":"both"}]

Blue eyes contain no blue pigment; they simply have very low melanin.

[{"selector":"#anim-200a6ab3-eb33-471c-9b88-808a20111248","keyframes":{"opacity":[0,1]},"delay":250,"duration":2000,"easing":"cubic-bezier(0.4, 0.4, 0.0, 1)","fill":"both"}]

Light scatters inside the iris, creating the illusion of blue—just like the sky.

[{"selector":"#anim-2a77c673-3c3e-412d-b877-04a5b8a31e34","keyframes":{"opacity":[0,1]},"delay":250,"duration":2000,"easing":"cubic-bezier(0.4, 0.4, 0.0, 1)","fill":"both"}]

Short-wavelength blue light reflects back, while longer wavelengths get absorbed.

[{"selector":"#anim-7b05a317-b114-405d-b130-fe974019c4e5","keyframes":{"opacity":[0,1]},"delay":250,"duration":2000,"easing":"cubic-bezier(0.4, 0.4, 0.0, 1)","fill":"both"}]

Brown eyes are the most common because they contain a high amount of melanin.

[{"selector":"#anim-89d76a74-7bc9-4116-b74a-362097cd402f","keyframes":{"opacity":[0,1]},"delay":250,"duration":2000,"easing":"cubic-bezier(0.4, 0.4, 0.0, 1)","fill":"both"}]

More melanin gives deeper colour and provides better protection from UV radiation.

[{"selector":"#anim-599fdaf3-a365-41af-b22b-9d0db15ff4b1","keyframes":{"opacity":[0,1]},"delay":250,"duration":2000,"easing":"cubic-bezier(0.4, 0.4, 0.0, 1)","fill":"both"}]

Green eyes occur when low melanin mixes with a yellow pigment called lipochrome.

[{"selector":"#anim-4e1c987f-334d-4b4d-82aa-a20557be9bf7","keyframes":{"opacity":[0,1]},"delay":250,"duration":2000,"easing":"cubic-bezier(0.4, 0.4, 0.0, 1)","fill":"both"}]

Hazel eyes shift between green, brown and gold due to uneven pigment distribution.

[{"selector":"#anim-770c9024-829e-4a10-a778-6b6959899bf7","keyframes":{"opacity":[0,1]},"delay":250,"duration":2000,"easing":"cubic-bezier(0.4, 0.4, 0.0, 1)","fill":"both"}]

Multiple layers in the iris scatter light differently, creating multi-toned effects.

[{"selector":"#anim-caca5a26-c6a9-4f22-ad3f-3c32335e6532","keyframes":{"opacity":[0,1]},"delay":250,"duration":2000,"easing":"cubic-bezier(0.4, 0.4, 0.0, 1)","fill":"both"}]

Eye colour is controlled by several genes—mainly OCA2 and HERC2 on chromosome 15.

[{"selector":"#anim-ec2a81da-8c6f-43ad-852f-a1e630444fa8","keyframes":{"opacity":[0,1]},"delay":250,"duration":2000,"easing":"cubic-bezier(0.4, 0.4, 0.0, 1)","fill":"both"}]