It's probably no secret that people are quite happy when they take a bit of "me time." But new research conducted at the University of Pennsylvania confirms that individuals are more content and their lives improve when they show a bit of selfishness.

However, past studies also show that people often put others before themselves, even at the expense of their own happiness. So why the discrepancy? According to researcher Jonathan Berman, it all has to do with guilt.

In other words, people will often happily spend money on themselves and feel good about it, but when confronted with the idea of donating to charity, spending in their own self-interest suddenly feels wrong.

To test the notion that forced selfishness is a good thing, Berman and colleague Deborah Small conducted three separate tests. They discovered that, without fail, participants felt happier when being selfish—but only when they were fully absolved from the responsibility of being charitable to others.

"People gain happiness from doing what is in their self-interest," the study says. "Yet much research casts doubt on this basic assumption. We argue that one reason why people do not feel happier with self-interested behavior is that doing so sometimes involves sacrificing the well-being of others along the way, and individuals often feel uneasy about making this trade-off."