What's the first thing a person notices about you? No, it's not your intricate updo, your killer cat eye, or your new outfit. It's your smile. Smiles have such a big impact on first impressions that they've been the subject of numerous studies, and all of them come to the same conclusion: the whiter and brighter the smile, the better.

A healthy, radiant smile is one of the most useful accessories in your arsenal. It can do everything from make your new lipstick color pop to convey to a prospective employer that you're the best candidate for the job. But if yellowing and unsightly stains take over your teeth, you squander one of your best assets.

With inexpensive whitening kits like Plus White 5 Minute Premier Teeth Whitening System, $11.39, getting a bright smile doesn't have to mean costly office appointments or super-sensitive teeth. "If done properly, whitening has no harmful or long-lasting effects to the teeth and gums," says New York City-based cosmetic dentist Dr. Marc Lowenberg of Lowenberg, Lituchy & Kantor. Plus White's kit comes with everything you need to get started, including an innovative needle-nose tube that allows for precise application and a StainGuard rinse that keeps your teeth whiter and brighter throughout the day. Better yet, it only takes five minutes out of your day.

Click ahead to see the benefits of a brighter smile and how you can get your brightest smile yet with zero pain.

Ever put on a bold, red lip only to smile in the mirror and realize your teeth have never looked yellower? Discolored and stained teeth often sabotage beauty looks by making the majority of lip colors look harsh rather than complementary. A punchy lip color draws attention to a yellow smile -- in a bad way. Getting a brighter smile enables you to experiment with on-trend shades like oranges and deep roses and look great. "You'll start noticing you can wear all of the lip colors you never thought were possible," says Dr. Jonathan B. Levine, a dentist who specializes in aesthetic dentistry in New York City. For your brightest smile yet, try picking a deep red lipstick with blue undertones.

Wrinkles, crows' feet and age spots get targeted in your anti-aging beauty regimen, but teeth may be giving away your age, too. As you get older, the outer layer of enamel begins to wear away, revealing a yellowish color. Factor in stains from multiple cups of coffee a day, a glass of red wine every night or smoking, and you're left with a dull smile that is just as telling as sagging skin. Never fear: You can easily turn back the clock by brightening up. "A white smile is the easiest way to look 10 years younger," says Levine.

"In a lot of cases, yellow or dark teeth tend to hold people back," says Levine. The less you smile, the more you miss out on opportunities to exude approval, power, friendship, attraction and even a positive outlook on life. "Smiling increases the production of serotonin [and] has been scientifically proven to elevate the mood of both the person giving the [smile] and the person receiving it," Levine explains. With a whiter and brighter smile, you're prone to smile more often and project more confidence. The end result? Way more self-esteem, no self-help books or motivational speakers required.

The confidence that comes with a brighter smile not only positively affects your personal life, it boosts your professional life as well. Numerous studies show that a bright smile, the key to a great first impression, has a direct effect on successful interpersonal interactions in a professional setting. In mock job interviews, prospective employers viewed candidates with whiter teeth as more professional, open, trustworthy and healthy. Not only were employers more likely to hire candidates with bright smiles, they were also more likely to offer them higher salaries.