Trends are a tricky thing. Witness: My sister, who lives in Chappaqua, NY, recently introduced my 11 year-old daughter to the most coveted little girl toy on the East coast -- the Rainbow Loom.

In her neck of the woods, the bracelet making contraption has been sold out for months and is all the rage with the under 16 crowd. We had never even heard of the thing, and it's not because we live in Podunk or some small tucked away town -- it's just that this monster trend had yet to hit Los Angeles. It has now. (And I secretly cajole myself into believing that my kid's instant obsession -- and her having proselytized it to all of her pals -- had something to do with that.)

Which is precisely the wrinkle when it comes to forecasting trends and honing in on what's going to become a bestseller; you never know what's going to catch on where -- and when.

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To have some fun with this phenomenon in the cosmetics realm, the ladies at Stylelist.com surveyed 50 department and beauty supply stores in 30 of our United States to see which items were selling best in the varying parts of the country. Then, they did the math and compiled a list of the top-selling beauty products du jour.

You can see the whole caboodle here, but, to give you a taste, here's a sampling of the results. How many best sellers are in your beauty arsenal?

Best-Selling Mascara: Benefit They're Real!, $23. This mascara (my own personal favorite) has become the go-to lash enhancer on the market.

Best-Selling Blush: NARS Blush in Orgasm, $29. This 2013 TotalBeauty Beauty Awards winner remains a staple in most women's makeup bag.

Best-Selling Primer: Smashbox Photo Finish Foundation Primer, $36. Heralded for creating a flawless canvas for foundation application, this perennial chart topper doesn't appear to have fallen out of anyone's favor.

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