Jeans are singing the denim blues as more people integrate yoga pants and leggings into their everyday attire.

Sales of jeans in the U.S. fell 6 percent to $16 billion last year, according to market research firm NPD Group. Sales for yoga pants and other active-wear increased by 7 percent to $33.6 billion.

Consumers have chosen to insert more comfort into their daily wardrobes. More formal attire is no longer required at many workplaces, schools and other public establishments.

"Active-wear is booming, with sales growth exceeding that of the apparel market as a whole," said Marshal Cohen, chief industry analyst for NPD. "And it's because consumers wearing active-wear not only go to the gym, in the gym, and from the gym, but they are working out, going out, and even hanging out in active-wear."

Even Levi Strauss, the inventor of blue jeans, has acknowledged the "athleisure" trend has hurt their business, according to CBS News. Levi is designing new, stretchier jeans to stay competitive across all its brands.

"If casualization is what everyone is looking for, we can push the innovation," James Curleigh, president of the Levi's brand, told CBS News.

The denim pants still account for 20 percent of annual sales at the nation's department stores, according to retail consultancy Customer Growth Partners. All active-wear sales make up 16 percent of the total apparel market, NPD Group revealed.

Corduroy pants gave jeans similar competition in the mid-1970s. Estimates showed that denim sales fell 3 to 4 percent, compared to a 10 to 12 percent rise in corduroy sales, according to NDP.