As the summer brings sweltering heat, office dress shifts. Skirts and sleeves are shorter, sandals are prevalent, and both seasoned professionals and the summer's crop of interns test the boundaries of casual dress.

But as office dress codes become more relaxed, some employers worry that the work ethic will weaken. Will wearing polo shirts to the office discourage employees from staying past 6 p.m.? Will dressing in khakis instead of a power suit make a manager less likely to invite clients to lunch? Will wearing sandals lessen someone's motivation to negotiate a deal?

Business consultant Andrew Jensen, who has studied the correlation between office wear and productivity, says that researchers, like managers, disagree on the matter of attire: "It comes down to office environment. In a more relaxed environment, casual dress works and doesn't have much impact. In a more traditional environment, casual dress does have an impact, especially when employees go too far."

Jensen of the Sozo Firm in Pennsylvania says that in some workplaces, bosses contend that the national trend toward business-casual wear can boost morale and camaraderie and even increase creativity by allowing workers to feel comfortable and happy. In others, supervisors say that business-casual can easily be abused and lead to sloppiness, laziness and a decrease in professionalism. "The dress code really needs to be customized depending who your customers are and how often you interact with them," Jensen says.

On a given day, what we wear to work can affect our focus, motivation and what we accomplish, says Mike Slepian, adjunct assistant professor at Columbia Business School and author of "The Cognitive Consequences of Formal Clothing." He says casual clothing makes workers think less abstractly and more concretely — useful for completing tasks focusing on details such as writing code or planning a product launch. He says that with formal dress, workers feel more powerful and ready to tackle higher-level abstract thinking.

In offices that have casual Fridays, some employees see their mood shift with the change in work attire. Georgi Pipkin, corporate manager of marketing at Baptist Health South Florida, dresses for the interactions planned for the day and finds that her outlook correlates with her clothing

While industry, geography and job title play a role in dress code, overall workplace attire increasingly has become more relaxed. Pantyhose are out, the once de rigueur suits are rare, and polo shirts have replaced ties. The movement toward business-casual is spurred in part by the influx of millennials in the workforce who prefer to dress down, according to Office Team, a national staffing service. "Millennials have seen Mark Zuckerberg in his T-shirts and jeans, and they believe what you wear does not define how successful you are going to be or whether it will impact business," says Angie Diaz Medina, of Baptist Health South Florida.

However, pushing the boundaries of business-casual too far can be problematic in any workplace. As a corporate trainer and Dallas-based business coach, Shontaye Hawkins works with companies across the country and suggests they provide employees photos of exactly what they consider business-casual. "You don't want to lose a potential client or customer because they come on a day someone is wearing flip-flops and decide your workplace is unprofessional," she says. "Dressing too sloppy can cost a business money."