You may have always been told that it's what's on the inside that counts – when it comes to getting ahead at work, that means brains. While advanced degrees and stellar performance are still key aspects of a promotion or raise in salary, studies show that beauty can also help you move up on the career ladder.

CEOs are more competent looking
Researchers from Duke University found that CEOs are more likely than non-CEOs to be rated as competent looking, and less likely to be classified as likeable. CEOs who look competent also earned more money than those who did not look this way, even though appearance had nothing to do with any of the companies' profitability.

This isn't the first time studies have shown a connection between beauty and wages, according to John Graham, a finance professor at Duke. Other studies have shown that politicians benefit from their looks during elections. This particular study proved that appearance plays a role at the corporate executive level, he said.

Fit people get paid more
Even in other sectors of the workforce, beauty and fitness have been proven to have a positive impact on an employee's paycheck. A study from New York University found that a 1 percent increase in a woman's body mass index results in a 0.6 percentage point decrease in her family income. Another study from the Journal of Labor Research reported that individuals who exercise regularly enjoy a 9 percent higher pay on average than those who do not. Although this does not give evidence of cause and effect, it makes a case for fitting a workout into your day for extra energy and productivity.

Happiness counts
Of course, these factors may just contribute to an employee's overall happiness and self-esteem, both of which have also been proven to have a positive effect on a worker's performance and salary. According to a study from Illinois Wesleyan University, individuals who had high levels of happiness and high self-esteem at a young age had greater incomes later in life. They also concluded that positive-thinking workers are often more productive. This, of course, can lead to raises, promotions and more.

Do you think appearance has played a role in your career? Should employers do more to ensure looks are not a factor in promotions?