Ageing and Eyes

Brown eye colour facts: What causes eyes to be brown?

Baby with brown eyes
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Brown eyes are more common worldwide than any other eye colour. But the prevalence of brown eyes varies significantly with geography.

Most people living in Africa and Asia have dark brown eyes. Dark brown eye colour also is very common in the Middle East. But in Europe, both the prevalence and shade of brown eyes vary significantly from region to region. In the UK, an estimated 22 percent of the population has brown eyes — including dark brown eyes, light brown eyes and honey brown eyes. If you include hazel eyes (sometimes called hazel brown eyes), the prevalence is even higher.

But the high prevalence doesn't mean all brown eyes look the same. There is plenty of variation in the appearance from person to person, and there are even health advantages to having brown eyes (more about that later).

What causes brown eyes?

Even though there are different eye colours, including less common blue eyes and green eyes, there is only one type of eye colour pigment. The amount of this pigment (called melanin) present in the iris of your eye determines the colour of your eyes.

Eyes with very little melanin in the iris are blue. Eyes with a bit more melanin are green, hazel or light brown. And those with a high concentration of melanin are medium or dark brown.

Eye colour is an inherited trait. But predicting eye colour from your family tree is more difficult than you might expect. In fact, there is evidence that up to 16 genes can influence eye colour.

So it's very possible for children in the same family to have different eye colours, and eyes that are not the same colour as those of their parents. Due to complex variations and interactions of genes, it's hard to say with certainty what colour eyes a child might end up with.

Also, the eyes of many Caucasian babies contain very little melanin at birth and will appear blue in the first few months of life. But within 12 to 18 months, more melanin can accumulate in the iris, causing eye colour to change from blue to green, hazel or brown.

Benefits of brown eyes

If you have brown eyes, you'll be happy to know that researchers have found the higher melanin content in your eyes is associated with a number of health benefits.

People with brown eyes may be less vulnerable to certain diseases. For example, people with brown eyes appear less likely to develop age-related macular degeneration than people with light-coloured eyes.

Also, people with brown eyes have a lower risk of type 1 diabetes and melanoma of the eye, compared with individuals with light blue eyes. And research at the National Hospital for Neurology and Neurosurgery in London  suggests individuals with blue eyes have a higher risk of hearing problems caused by environmental noise pollution compared with coworkers with brown eyes. The study authors felt melanin pigment may help protect nerves in the brain from noise-induced damage.

But it's not all good news for people with brown eyes.

Research at the University of Pittsburgh  found that women with dark-coloured eyes seemed to experience more pain when giving birth compared with mothers with light-coloured eyes. The women with light-coloured eyes also had less anxiety, depression, negative thoughts and sleep disturbances than the women with brown eyes.

Also, researchers in Australia  found that people with dark brown irises were more likely to develop cataracts than people with lighter-coloured eyes. So be sure to wear sunglasses that protect your eyes from UV radiation outdoors if you have brown eyes. (In most cases, polarized sunglasses offer the greatest comfort in bright sunlight.)

Brown eyes: More trustworthy?

Did you know that having brown eyes may make you appear more trustworthy?

In research performed in the Czech Republic , university students were asked to look at photographs of 80 fellow students (40 males and 40 females, ages 19 to 26 years). Participants in the study were asked to rate the photographed students for trustworthiness on a 10-point scale.

The students who were photographed were told to assume neutral, non-smiling expressions and not to wear any make up or jewelry. All photos were cropped so that the eyes were always horizontally at the same height with a standard length of neck visible. Only photos of individuals with blue eyes or brown eyes were used in the study. Photos of students with hazel or green eyes were excluded.

Results of the study revealed that people with brown eyes were perceived as significantly more trustworthy than those with blue eyes.

But it's a little more complicated than that.

The researchers found a relationship existed between eye colour and face shape, and that the shape of a person's face plays a key role in the perception of trustworthiness.

Brown-eyed faces tended to have a rounder and broader chin, a broader mouth with upward-pointing corners, relatively bigger eyes, and eyebrows closer to each other. In contrast, blue-eyed faces were characterised by a more angular and prominent lower face, a longer chin, a narrower mouth with downward-pointing corners, relatively smaller eyes and rather distant eyebrows.

"Brown-eyed individuals tend to be perceived as more trustworthy than blue-eyed ones," explained the study authors. "But it is not brown eyes that cause this perception. It is the facial morphology linked to brown eyes."

Eye colour options

Despite the advantages associated with brown eyes, if you'd like to try other eye colours, you can.

There is a wide variety of coloured contact lenses for brown eyes — and these appearance-changing coloured lenses are available even if you don't need correction for nearsightedness, farsightedness or astigmatism. There are even coloured contacts for brown eyes that can change the colour of your eyes to light blue if that's what you desire.

Not ready for contacts but want to know other ways to make your brown eyes "pop?"

If you wear glasses, ask your optician to show you how different frame colours can complement and enhance your brown eyes. Also, choose lenses with an anti-reflective coating to help showcase your eye colour. AR coating eliminates annoying reflections in your glasses, allowing others to see the beauty and expressiveness of your brown eyes.

Also, spend time with a professional aesthetician to discover the best eye shadow and make up for brown eyes. The right choices for you will depend on a number of factors — including your hair colour and skin tone as well as the depth of the pigment in your brown eyes.

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