Denim was once king of American causal fashion, but it seems that jeans are about to be dethroned.

Sales of jeans are down 6 percent year-over-year, according to analysts at the NPD Group. While that may not seem like much, it’s big for the industry.

“It’s rare for denim to take such a dramatic drop,” Marshal Cohen, chief industry analyst of The NPD Group told NBC News.

One reason: cost. Sales of high-end jeans priced over $75 were down by 18 percent in 2013, according the NPD Group. On the West Coast, those numbers were even more dramatic, with high-end jeans falling by 40 percent in 2013.

Unlike pricey jeans, yoga pants and athletic wear can be purchased for as little as $10. Called “athleisure,” yoga and gym clothes are becoming the new go-to casual wear for women from teenagers to adults.

Piper Jaffrey’s “Taking Stock of Teens” biannual survey shows teens turning from brands – like Levi’s and True Religion – and towards athletic brands, such as Lululemon and Athleta.

If you aren’t big on following trends, now may be the time to buy jeans. Retailers, such as American Eagle Outfitters and H&M, are slicing prices on their jeans.