Hazel eyes

Hazel eyes can be dark, light, or somewhere in between. Some people have hazel brown eyes, and some have hazel green eyes. Others may have flecks of brown, gold, green, or even blue. Read on to learn how this unique shade is possible, and just how rare it is around the world.

How eye colour is determined

Eye colour is the unique hue seen in the iris (the coloured part of the eye). It is determined by genetics and a pigment in the body called melanin. This may sound simple, but many pieces have to come together, in just the right way, to make your eyes look the way they do.

Melanin

Melanin is a pigment that gives your hair, skin, and eyes distinctive tones. The more melanin you have, the darker your complexion and features are likely to be. The types and levels of melanin your body produces and distributes are largely determined by your genetic makeup.

Genetics

Contrary to past (and popular) belief, the genetics behind eye colour are much more complex than the idea that brown eyes are dominant and blue eyes are recessive. Experts have since determined that there are many different genes, as well as genetic mutations, that can influence eye colour.

What causes hazel eyes?

Like other shades, the hazel eye colour is determined by genetics and melanin. But it’s the way light interacts with the melanin in the iris that makes hazel eyes so special.

The iris has two layers — front and back — in which melanin may be found in varying types and amounts. Blue and green eyes have a more uniform colour because the melanin in the iris is spread out evenly between the two layers. Hazel eyes have an uneven distribution, which makes multiple hues in the iris possible.

Because of the variation of melanin levels and types, hazel eyes may contain a mixture of green, brown, gold, and even blue shades or flecks throughout the iris.

Hazel eyes have less melanin overall than brown eyes, which means they absorb less light. Any unabsorbed light is scattered across the iris and reflected to display the hazel eye colour that people see.

Medical reasons for hazel eyes

Eyes may have a hazel appearance as the result of a specific condition or medication, including:

Iris freckles – These may appear due to sun exposure, similar to freckles on the skin. Freckles on the iris can sometimes give a person’s eye colour a different look.

Heterochromia – This is when your irises are different colours. Some people may have one brown eye and one blue (or another colour), or one eye that is partly blue and the rest is brown (as well as the other eye). Eyes with central heterochromia (different-coloured rings around the pupil) are often confused with hazel eyes.

Glaucoma medication – A class of drugs known as prostaglandins is sometimes given to treat glaucoma. Hazel eyes may become more brown when this type of medication is used.

Other medical conditions can alter the appearance of your eye colour. For example, cataracts can make the eyes look cloudy. And inflammation in the eye — called uveitis — can make the eye look very red. If uveitis affects the iris, the redness may even affect your eye colour.

If you notice a change in your eye colour, contact your eye doctor as soon as possible. Some issues that affect the appearance of your eyes are nothing to worry about, but some can be symptoms of a serious medical condition.

Do hazel eyes change colour?

Hazel is one of the rarest eye colours, accounting for only about 5% of the world’s population. That’s compared to the 8% to 10% of the population that has blue eyes, and the majority of the population (70% to 80%) that has brown eyes.

Some other rare eye colours include amber, which represents 5% of the global population; grey, which represents 3%; and green, which represents just 2%.