Hazel eyes get their distinctive multi-colored appearance from a specific combination of pigment, light scattering, and genetics. Unlike brown eyes, which are dominated by a single dark pigment, hazel eyes contain a moderate amount of melanin that interacts with light in the iris to produce shifting tones of brown, gold, and green. About 5% of the world’s population has hazel eyes, with a higher concentration in the United States, where roughly 18% of people have them.
Melanin and Light Create the Color
Eye color comes down to two things: how much pigment sits in your iris and how light behaves when it passes through. The iris has multiple layers, and the one that matters most for color is the stroma, a mesh of colorless collagen fibers that can also contain varying amounts of melanin. Brown eyes have dense melanin throughout the stroma, absorbing most light. Blue eyes have almost none, allowing light to scatter off the collagen and bounce back as blue. Hazel eyes fall in between.
Two types of melanin play a role. Eumelanin is a dark brown-black pigment, while pheomelanin is a red-orange pigment responsible for the warm gold and amber tones in hazel and green eyes. Hazel irises contain more melanin than green or blue eyes but less than brown, and the ratio of eumelanin to pheomelanin determines whether the eye leans more golden-brown or greenish.
The second ingredient is light scattering. When light enters the stroma and hits the fine collagen fibers, shorter wavelengths (blue light) scatter more than longer ones. This is called the Tyndall effect, similar to the way the sky appears blue. In hazel eyes, some light gets absorbed by the melanin (producing brown and gold tones) while some scatters off the stroma (producing a blue-green hue). The combination of absorbed and scattered light is what creates that layered, multi-toned look, often brown near the pupil fading to green or gold at the outer edge of the iris.
How Hazel Differs From Green and Brown
The line between hazel and green eyes comes down to melanin concentration. Green eyes have relatively little melanin in the front layer of the iris, so the Tyndall effect dominates and the eye appears green with minimal brown. Hazel eyes have more melanin than green but less than brown, producing a visible mix of both warm and cool tones. Brown eyes have enough melanin to absorb most incoming light, so scattering effects are overwhelmed. Cleveland Clinic describes hazel eyes as “a combination of brown, gold, or green,” which captures the spectrum. If you see distinct brown or amber alongside green in the same iris, that’s hazel rather than pure green.
The Genetics Behind Hazel Eyes
Eye color was once taught as a simple dominant-recessive trait, but it’s actually controlled by multiple genes working together. The two most influential genes sit near each other on chromosome 15: OCA2 and HERC2. OCA2 produces a protein involved in melanin production, and HERC2 acts as a switch that can turn OCA2’s activity up or down.
For hazel eyes specifically, a variant in the OCA2 gene called rs1800407 has been associated with green and hazel eye color in people of European descent. This variant causes a single amino acid change in the OCA2 protein, slightly altering how much melanin the iris produces. It’s not one gene flipping a switch to “hazel,” though. At least 16 genes contribute to eye color, which is why two brown-eyed parents can have a hazel-eyed child, and why hazel eyes can look so different from one person to the next. The specific blend of genetic variants you inherit determines exactly how much melanin ends up in each layer of your iris, and therefore where on the brown-to-green spectrum your hazel falls.
Why Hazel Eyes Seem to Change Color
People with hazel eyes often notice their eyes look different colors depending on the situation. This isn’t your imagination, but it’s also not your pigment literally changing. Because hazel eyes depend on both pigment absorption and light scattering, anything that alters the light hitting your iris changes the balance between those two effects.
Bright outdoor sunlight emphasizes the warm gold and brown tones by illuminating the melanin. Indoor or overcast lighting can make the green and blue tones more prominent because scattered light becomes more visible relative to absorbed light. The color of your clothing, makeup, or surroundings can also shift what an observer perceives through simple color contrast.
Your pupil size plays a role too. When your pupils dilate in dim light or during strong emotional responses like stress or excitement, the iris tissue compresses, packing the pigment into a smaller visible area. This can make the color appear darker or more intense. When your pupils constrict in bright light, more of the iris is exposed, and light has more stroma to scatter through, which can make hazel eyes appear lighter or greener. These are purely optical effects. The actual pigment in your iris stays the same throughout the day.
When Hazel Eyes Develop
Most babies are born with blue or gray eyes because melanin production in the iris hasn’t fully ramped up yet. The most significant color changes happen between 6 and 9 months of age as melanin is deposited into the stroma. By that point, a baby’s eye color has usually settled into something close to its permanent shade. Subtle shifts can continue until around age 3, though, so a toddler whose eyes look blue-green at 6 months may end up with distinctly hazel eyes a couple of years later. After early childhood, hazel eye color remains stable for life in most people.
Light Eyes and UV Risk
The same lower melanin levels that give hazel eyes their color also mean less natural protection against ultraviolet light. Melanin in the iris acts as a shield, absorbing UV radiation before it reaches deeper eye structures. With less of that shield, lighter eyes are more vulnerable to certain types of damage over time.
A Dutch study published in the journal found that people with green or hazel eyes had roughly 3.6 times the risk of developing uveal melanoma (a rare cancer of the eye’s inner layers) compared to people with brown eyes. People with blue or gray eyes had a smaller but still elevated risk at about 1.4 times. The pheomelanin that gives hazel and green eyes their warm tones may actually contribute to this vulnerability. Unlike eumelanin, pheomelanin has a lower threshold for producing reactive oxygen species when exposed to light, and it can generate low levels of genotoxic damage that accumulate over decades.
This doesn’t mean hazel eyes are fragile or that eye cancer is likely. Uveal melanoma is rare regardless of eye color. But it does mean that wearing UV-blocking sunglasses outdoors is especially worthwhile if your eyes are on the lighter end of the spectrum.