Inside Sephora, where nail polishes and perfumes abound, Dwight O’Neal holds out a makeup brush to dab his brand’s illuminizer on a young woman. Over the next few weeks, O’Neal will travel to Sephora stores throughout the Southeast prettying potential customers to pump up sales of Josie Maran products. With his intense schedule during the holidays, taking a vacation day is out of the question.

For O’Neal, an educator and sales support representative with Josie Maran Cosmetics, that means thinking strategically and using his vacation time in February, rather than forfeiting days off at year end.

As 2012 draws to a close, the question looms: Are you going to accidentally forfeit vacation days?

For an increasing number of American workers, the answer is yes.

“Now is the time of year that everyone should take note of his or her company’s vacation policy,” says employee benefits expert Joanne Apice. You should know if you can carry over vacation days and if so, how many.

A survey by Harris Interactive found that by the end of 2012, Americans will leave an average of 9.2 days of vacation unused, up from 6.2 days last year. It also found profits per employee are at a 10-year high, mostly because workers are cramming in more hours.

O’Neal says in December he crams in hours at Sephora by choice. He loves his job showing customers how to use Josie Maran’s organic cosmetics and wouldn’t want to take a day off during busy season even if he could. “In retail, December is a blackout period but that’s OK with me. I love being on the floor, interacting with customers.”

Others say they, too, try to be strategic about vacations, well aware of policies on “use them or lose them” and end-of-the-year blackout periods in industries such as hospitality, retail and healthcare. But inevitably, there are those who lose track of where they stand with vacation days.

“There are workers who are scrambling to get days off scheduled,” Apice says. “When you have multiple employees in that situation and you still have work that needs to be done, it is a challenge to balance scheduling and management of the department.”

Yet, for some workers, particularly at high levels, there’s a reluctance to take time off. An increasing number of people say they can’t afford to take all the vacation allotted to them because work piles up. Others conclude that they are just too busy to take time off or don’t want to send the signal that they are not committed.

Peter Mendez, a finance services executive, says he will be among those who leave vacation time unused in 2012, mostly because he fears the mountain of work that awaits upon return. “It is too painful coming back to 2,000 emails.”

Forfeiting vacation time happens even as American bosses encourage employees to take their earned time off. According to an Expedia survey, the majority of Americans workers said their bosses support taking their allotted time off, with only 5 percent who said their bosses weren’t supportive. “Employers give vacation time to recharge so that when you come back you are refreshed and can perform better,” Apice said.

John Morrey, general manager of Expedia.com, said in a statement, “Your vacation days are not a gift, not a luxury. They’re yours to use. Studies consistently show that an ideal work-life balance leads to happier and more productive employees.”