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For one, don't buy them at the mall.

Changing your hair color is an easy transformation that millions of women make every year, but switching your eye color requires a lot more research and planning beforehand — or it should, at least.

Selena Gomez (above) recently wore blueish gray contacts at the Victoria's Secret Fashion Show — and she looked beautiful (although we love her natural brown eyes, too.) But we bet she got hers from a doctor or other reputable source. The problem is a lot of people jump onto the colored contact lenses bandwagon without learning about the risks, sometimes with disastrous results. So if you want to switch up your eye color, here's what you need to know.

We've all seen people wearing them, but most people don't understand what they actually are. "Colored contact lenses are lenses that have been dyed with biologically compatible dyes in order to make the surrounding portion of the lens opaque, while the center remains transparent so the wearer can see," explains Dr. Kerry Assil, eye surgeon and Medical Director of the Assil Eye Institute in Los Angeles. They can be worn for cosmetic reasons, including novelty purposes, as well as for therapeutic reasons by people who have had ocular injuries and need contacts to assist their eyes in blocking out excess light.

Dr. Assil recommends always purchasing your contact lenses from a specialist who can assess and monitor your usage, even if they aren't prescriptive. But what about novelty lenses? some might ask, particularly around Halloween. "Special effects lenses should be even more tightly monitored by a specialist," emphasizes Dr. Assil. In fact, one Michigan teen nearly went blind after she purchased cosmetic contact lenses from a non-medical pro at the mall — the lenses ripped out the top layer of her cornea. Your eyes are one of the most important organs on your body — would you really want to skimp on caring for them and risk losing your sight?

While they make look just as ultra-thin as a typical contact lens, Dr. Assil says that colored contacts "tend to be thicker." This can cause some discomfort — and is another big reason to get them fitted by a pro. Plus, if you find out they're just not for you while still at the doctor's office, you won't waste a bunch of money on a box of contacts that you won't be able to wear or return.

Though colored contacts can be a lot of fun, it's important to remember that your eye is incredibly delicate. "These lenses tend not to be as biologically forgiving as regular contacts with regard to oxygen transmission to the eye," says Dr. Assil. "Worn for a long period of time, they can increase the risk of infection." And if you're getting your lenses without consulting an eye doctor beforehand, you could be putting yourself even further at risk.

Just like regular contact lenses, Dr. Assil advises cleaning colored contacts on a daily basis, never letting anyone wear them besides you, and never leaving them in overnight. These aren't just paranoid precautions — there are real-life horror stories that can back up the need for proper care. For example, after storing her contacts in a glass of solution rather than a case, a young woman in England woke up to find her eye was severely swollen. When she went to the doctor to figure out the problem, she was told it was an amoeba that had started eating away at her cornea as a result of her poor contacts care — and she had to endure an excruciating recovery process to combat it, all because she didn't store her lenses in a proper place.

That's right: Some people are actually going under the knife to change their eye color from brown to blue. Though the procedure is not approved in the United States, Dr. Assil says that he has seen many people head to other countries for the operation — sometimes resulting in permanent damage. "Cosmetic contact lenses can be exciting and rewarding when worn and fitted properly," says Dr. Assil. "They're much safer than some of the touted surgical options that go into the eye and affect its natural pigment by either inserting material or trying to leech the pigment out of the eye." If you truly want to alter your eye color, stick to lenses — just so long as you're willing to buy and wear them responsibly.