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Eyes can tell a lot about a person: what they’re thinking and feeling, of course, and whether they’re lying or loyal. This is perhaps why the adage “the eyes are the window to the soul” rings true. But though your eye color may seem rather superficial, it can say a lot about your health too, in ways you may not have been aware, Medical Daily reports.

This is because a variety of genes go into deciding your eye color. There aren’t just two genes — one for blue eyes and one for darker eyes as many scientists previously thought — but rather, there are up to 12 to 13 gene variations that can decide color. These genes linked to eye color are often at play in your body in different ways, which is why eye color can be a determinant of other health aspects. “These genes do other things in the body,” Dr. Jari Louhelainen, a senior lecturer in biomolecular sciences at Liverpool John Moores University, told the Daily Mail. “One of them, NCX-4, which is linked to darker eyes, controls many proteins, of which one has recently been linked to pain.”

Our skin, hair, and eyes all get their color from a group of natural pigments called melanins. The amount of melanin in your iris defines whether you’re born with green, blue, or brown eyes. People who are born with a lot of melanin in the stroma of the iris tend to have brown eyes, while people with less melanin have green or hazel eyes, and finally, having no melanin typically leads to blue eyes. Eye color is unique for every individual (no one has the same exact color as anyone else) and it changes constantly, shifting shades over the period of a lifetime depending on your genes, diseases, and age. Below are some of the things your eye color can tell about you.

Your ancestry

In 2008, scientists discovered that everyone who has blue eyes is genetically linked to the same common ancestor, a person who experienced a genetic mutation sometime between 6,000 and 10,000 years ago. Before this mutation, every human had brown eyes. “A genetic mutation affecting the OCA2 gene in our chromosomes resulted in the creation of a ‘switch,’ which literally ‘turned off’ the ability to produce brown eyes,” said Hans Eiberg, a lead researcher of the study at the Department of Cellular and Molecular Medicine at the University of Copenhagen, in a press release. In short, this “switch” limited the OCA2 gene from producing melanin, which led to blue color in eyes. So, if you’re blue-eyed, it’s likely that you may share a common ancestor with all the other blue-eyed people out there.

How we handle pain

Some scientists may argue that your eye color can tell you something about how your pain tolerance. One study published earlier this year found that out of 58 women, those with light-colored eyes seemed to experience less pain when giving birth compared to those with dark-colored eyes. Not only did women with light-colored eyes experience less physical pain, but they also reportedly had less anxiety, depression, and negative thoughts. “Human pain is correlated with multiple factors like gender, age, and hair color,” said Dr. Inna Belfar, a geneticist at the University of Pittsburgh who was a leading author of the study, at the American Pain Society's annual meeting in June. “Researchers have found that red hair is associated with resistance to anestheticsm and also to increased anxiety, and darker eye color has been reportedly found to correlate with increased physiologic reactivity and drug-induced pupil dilation."

Other studies have hinted that your eye color may indicate something about how well you can handle booze, too. In the past, researchers have found that people with light-colored eyes were more likely to abuse alcohol than people with dark-colored eyes because they could handle larger amounts of alcohol.

A window to your soul — and personality

A study conducted in Australia found that people with lighter eyes could be less “agreeable,” and far more competitive, than people with darker eyes. Agreeableness is a personality factor that is typically associated with empathy, friendliness, generosity, and compassion. After examining 336 participants, researchers from two different universities in Australia found that people with darker eyes were more “agreeable” than North Europeans with blue eyes, though the same association didn’t hold true for Europeans in general. This may sound like a stretch, and more research will be needed to solidify the claim, but researchers believe it may have something to do with our evolutionary roots — thousands of years ago, our Northern European ancestors found light-colored eyes more attractive and ideal for mating. Thus, it's possible that blue-eyed people ended up having more of a competitive edge, at least in Northern Europe.

Trust

Could it be possible that people with brown eyes are more trustworthy than people with blue eyes? In a recent study, researchers had participants rate facial photographs of 40 female and 40 male students on how trustworthy they appeared. Brown-eyed people were significantly more likely to be perceived as trustworthy than people with blue eyes. But the level of someone's perceived trustworthiness could also be influenced by facial shape; the researchers found that "although the brown-eyed faces were perceived as more trustworthy than the blue-eyed ones, it was not brown eye color per se that caused the stronger perception of trustworthiness but rather the facial features associated with brown eyes," they wrote in the abstract.

Disease, aging, and trauma

In addition, some studies have linked specific eye colors to diseases like diabetes, melanoma, and vitiligo. A 2012 study out of the University of Colorado School of Medicine found that people with blue eyes are less likely to have vitiligo, a skin condition that results in the loss of brown pigment from certain areas of the skin and leaves white blotches across some parts of the body. The study examined 3,000 Americans of non-Hispanic European ancestry who had vitiligo, and found that 43 percent had tan or brown eyes, while 27 percent had blue or grey eyes. This was quite different from the distribution of eye color among Americans of European descent, where 52 percent have blue or grey eyes, and only 27 percent have brown or tan eyes.

People's eyes may change hues depending on how bloodshot they are or what shirt they're wearing, but having each eye be a different color — a condition called heterochromia — can also be indicative of certain diseases, such as Horner's syndrome, Fuch's heterochromic iridocyclitis, or pigmentary glaucoma. In addition, people with late-stage diabetes might notice their eyes darkening.

Having lighter eyes may also mean that you're more sensitive to the sun's UV rays, since they contain less pigment to protect them. As a result, those with blue, grey, or green eyes may have an increased risk for melanoma of the uvea, which is the middle layer of the eye. "People with light iris color need to be more diligent in wearing UV-protected sunglasses," Dr. Ruth Williams, president-elect of the American Academy of Ophthalmology, told Everyday Health.

So, not only are your eyes your own personal window to the visuals and colors of the world, but they're a way for your body to tell a story of your own. As Karel Kleisner, an eye researcher from Charles University in Prague, says: "Eyes are not only for seeing, but also to be seen."