How Rare Are Hazel Eyes and What Causes Them?

Hazel eyes are uncommon worldwide, about 1 in 20 people, yet in the United States they are closer to 1 in 5. The color isn’t made by a single green or hazel pigment. It comes from a moderate amount of brown and lighter reddish-yellow pigment spread unevenly across the iris, plus light scattering that adds green tones. That’s why the same eyes can honestly look different from room to room, and that shifting is part of what defines hazel.1WorldAtlas. The World’s Population By Eye Color2World Population Review. Eye Color Percentage by Country

How Rare Hazel Eyes Really Are

About 5% of the world’s population has hazel eyes.3WorldAtlas. The World’s Population By Eye Color In the United States the share is about 18%, close to 1 in 5.4World Population Review. Eye Color Percentage by Country Brown is by far the most common eye color worldwide, which leaves every lighter color a small slice of the global total. Green is generally considered rarer than hazel worldwide, and blue is common mainly in northern Europe.

Hazel eyes are most common in North Africa, the Middle East, Brazil, and among people of Spanish heritage.5WorldAtlas. The World’s Population By Eye Color Eye color overall is most varied in people of European descent.6PubMed. Intraspecific eye color variability in birds and mammals: a recent evolutionary event exclusive to humans and domestic animals

Counts of hazel eyes are fuzzy, because there is no official cutoff between hazel, green and light brown. People usually label their own eyes, and the same eyes may be called green by one person and hazel by another. Surveys rely on those self-reports or on quick visual sorting, and neither uses a measured standard, so two surveys of the same population can disagree. Published shares are best read as ballpark figures.

What Gives Hazel Eyes Their Color

Eye color comes from melanin, the same pigment found in skin and hair. In the eye it sits in the iris, the colored ring around the pupil.7All About Vision. Eye Color: Cause, Genetics, Changes & All Possible Colors Melanin comes in two kinds: a dark brown-black type and a lighter reddish-yellow type.8All About Vision. Eye Color: Cause, Genetics, Changes & All Possible Colors Dark brown eyes have much more of the dark type, and much more pigment overall, than hazel, green or blue eyes.9PubMed. Characterization of melanin in human iridal and choroidal melanocytes from eyes with various colored irides In dark brown eyes the dark type outnumbers the light one about 15 to 1, while in hazel or blue-green eyes the ratio is closer to 1 to 1.10PubMed. The ultraviolet absorption coefficient of melanosomes decreases with increasing pheomelanin content

The reddish-yellow pigment is lighter and warmer than the dark type, so an eye with a more even blend of the two lands on a golden or amber-brown tone instead of deep brown. Because hazel has far less of the dark type, the iris is thin enough in pigment for other effects to show through.

Hazel and brown eyes contain about the same number of pigment-making cells.11JAMA Network. Melanocytes and Iris Color: Light Microscopic Findings The difference lies in what those cells produce, not how many there are.12PubMed. Characterization of melanin in human iridal and choroidal melanocytes from eyes with various colored irides

Hazel eyes contain no green pigment.13Gardner Eye Care. How Rare Are Hazel Eyes and What Causes Them? Every blue or green tone comes from light. Light scattering in the iris, the same effect that makes the sky blue, adds a bluish tint, and that blue mixing with yellowish-brown pigment reads as green.14Wikipedia. Eye color

Thin pigment lets more blue through and gives green, while heavy pigment hides the blue and gives brown. Hazel has thin and thick patches side by side. Pigment is often thicker near the pupil, so hazel eyes look light brown in the center and greener toward the edge.15All About Vision. What Causes Hazel Eyes?

Why Hazel Eyes Seem to Change Color

Hazel eyes often appear to shift color in different lighting.16WorldAtlas. The World’s Population By Eye Color Uneven pigment and light scattering mean the iris looks different depending on the light and the viewing angle.17FYidoctors. How Rare Are Hazel Eyes? Genetics & Science

Warm indoor bulbs give off more yellow and orange light, which the brown and gold parts of a hazel iris reflect strongly, so the eye reads as brown or amber. Daylight or an overcast sky is cooler and bluer. It adds more of the short wavelengths that the iris scatters, so the green becomes more noticeable.

Surroundings matter too. Colors near the eye can reflect onto the iris and make matching tones seem stronger, which is why a green shirt can make hazel eyes look greener. Eye makeup works partly by contrast: a purple or plum shade can make green and gold tones stand out against it. Pupil size plays a part as well, since it changes how much of the brown inner ring shows.

Hazel, Green, or Brown

Eye color runs as a continuum, from a small brown ring around the pupil to nearly all brown with a few green flecks at the edge.22PubMed Central. Classification of iris colour: review and refinement of a classification schema There’s no strict line where green ends and hazel begins.

To check your own eyes, stand by a window in natural daylight rather than under a lamp. Hold a phone camera close or use a mirror. Look for a brown or gold ring around the pupil, then note whether the outer part is green, brown or both. Check in two or three lights before deciding.

Indoor bulbs are typically yellowish and shine from above, which pushes the iris toward brown and can cast shadows from your brow. Window light is spread evenly and shows the iris more accurately.

The brown or gold in a hazel eye can show up as a ring around the pupil, scattered flecks or radiating streaks, and the pattern differs from person to person. Green eyes can have a little gold, so a few flecks alone don’t decide it; the overall impression of how much of the iris is more than one color matters more. A brown eye can look warm and golden in sunlight but stays brown across the whole iris.

How Genes Produce Hazel Eyes

A switch-like stretch of DNA in a gene called HERC2 controls how active a neighboring pigment gene, OCA2, is in the iris.23PubMed Central. A single SNP in an evolutionary conserved region within intron 86 of the HERC2 gene determines human blue-brown eye color When that switch turns OCA2 down, the iris makes less pigment, which leads to blue eyes.24PubMed Central. A single SNP in an evolutionary conserved region within intron 86 of the HERC2 gene determines human blue-brown eye color A partial turn-down leaves a middle amount of pigment, the range where green and hazel eyes appear.

Several separate variants in this same region each affect eye color.25PubMed Central. Investigating the genetic architecture of eye colour in a Canadian cohort In people of European descent, HERC2 and OCA2 interact in deciding whether eyes are hazel.26PubMed Central. Gene–gene interactions contribute to eye colour variation in humans One OCA2 variant is linked specifically with green or hazel eyes.27PubMed Central. Forensic DNA Phenotyping: Genes and Genetic Variants for Eye Color Prediction Many genes nudge pigment up or down a little, and their combined effects create the range of shades. Hazel is a midpoint the combination often lands on.

Brown eyes aren’t truly dominant and blue eyes aren’t truly recessive.28Advances in Anthropology. The Puzzle of European Hair, Eye, and Skin Color A single copy of the blue-eye variant usually produces an in-between shade like green or hazel, and even two copies don’t always produce blue eyes.29Advances in Anthropology. The Puzzle of European Hair, Eye, and Skin Color The classic school rule said two blue-eyed parents could only have blue-eyed children, but real eye color involves several genes and a graded amount of pigment, so they can occasionally have a child with a different color.

For your children, this means two hazel-eyed parents can have kids with brown, hazel, green or blue eyes. Parents can only estimate likelihoods, not predict a child’s color.

When Babies Get Hazel Eyes

Babies who end up green or hazel often look blue or gray for the first several months.30Vision & Learning Center. Baby Eye Color: How and When It Changes Golden or brown flecks then develop as pigment builds.31Vision & Learning Center. Baby Eye Color: How and When It Changes Eye color can keep shifting for several years, because a little more pigment can turn blue to green or hazel.32Pampers. When Do Babies’ Eyes Change Color? Uncover the Answer

At birth the iris has often not yet built up much pigment, so scattered light gives the eyes a blue or gray look. Pigment-making cells keep working after birth, and pigment gradually accumulates over the following months.

For a baby heading toward hazel, the first sign is often a ring or patch of gold or brown near the pupil. That tint can then spread outward through the iris, and the blue-gray fades into green, with brown or gold flecks remaining. The process is gradual, so a parent may only notice it by comparing recent photos with earlier ones. Many children settle by their toddler years, some later.

Can Hazel Eyes Change Color in Adults

Some eye drops used for glaucoma, such as latanoprost, can darken the iris.33PubMed. Side effects associated with prostaglandin analog therapy People with hazel eyes seem especially likely to get this darkening,34PubMed. Mechanism and clinical significance of prostaglandin-induced iris pigmentation and the highest rates occurred in green-brown and yellow-brown eyes.35PubMed. The incidence and time-course of latanoprost-induced iridial pigmentation as a function of eye color In a year of treatment, about 1 in 10 to 1 in 4 patients saw it, depending on the country.36PubMed. The incidence and time-course of latanoprost-induced iridial pigmentation as a function of eye color It typically appears around 6 months, spreading outward from the pupil, and about two-thirds of people who develop it notice it.37PubMed. The incidence and time-course of latanoprost-induced iridial pigmentation as a function of eye color

These drops increase the amount of pigment made by the iris cells; they don’t add new cells or stain the tissue. Irises with a mix of brown and green or yellow have room to gain pigment visibly, which helps explain why hazel is among the most affected. Because the pigment builds up, the darkening is generally regarded as permanent even if the drops are later stopped.

If you’re prescribed these drops, ask your eye doctor whether yours can change eye color. If only one eye is being treated, the colors may become mismatched. Don’t stop glaucoma drops without talking to your doctor, since protecting your vision comes first.

Other lasting color changes are a separate matter. A new change in one eye can follow injury or inflammation, and it can occasionally signal a growth inside the eye, so it deserves an eye exam.

Do Hazel Eyes Carry Any Health Risk

People with green, gray or hazel eyes have about 2.5 times the risk of melanoma inside the eye compared with brown-eyed people.38Cancer Research. Uveal Melanoma in Relation to Ultraviolet Light Exposure and Host Factors This cancer is rare, though, so the added risk to any one person stays small.

The lighter reddish pigment may handle light-induced stress and aging less well than the dark brown type.39PubMed Central. Iris Colour and the Risk of Developing Uveal Melanoma This is a possible explanation, not proven. Frequent sunburn and eye burns from welding or snow raise the risk further.40Cancer Research. Uveal Melanoma in Relation to Ultraviolet Light Exposure and Host Factors

Practical protection is simple. Wear sunglasses labeled 100% UV protection, use proper eye shields for welding and tanning lamps, and wear goggles on snow and water. Regular eye exams can also spot growths inside the eye.