8 big beauty sins: Cosmo got pro advice for rehabbing bad beauty behavior (we're all guilty of some). Now you can go about Looking hot, the right way.(COSMO BEAUTY BOOK)

[1] Nibbling On Your Cuticles

WHY IT'S A NO-NO: Torn cuticles lead to hangnails and infections, says Jessica Vartoughian, owner of Jessica Nail Clinic in Los Angeles.

REHAB: Keep the skin around your nails moisturized, says Vartoughian. "If it's hydrated, you'll have fewer snags and be less tempted to pick at it." Rub a thick cream or oil into your cuticles daily and massage them with an exfoliator every few days. Try OPI Skin Renewal Scrub, $8.95. Also, push overgrown skin back with a cuticle stone after showering, when they're soft. We like Revlon Expert Effect Cuticle Stone, $2.99. You can also try a bitter-tasting nail polish designed to discourage the habit.

[2] Swapping Your Strand Shade Frequently

WHY IT'S A NO-NO: Trading your tress tint occasionally is okay, but dyeing it too often can make it weak and lead to an identity crisis. Sure, celebs like Rachel McAdams and Ashlee Simpson constantly switch up their hair hue, but they do it for a movie or to capture attention on the red carpet. And they put in major moolah and extra TLC to undo or hide the damage.

REHAB: First, try diverting your desire for novelty from hair color to makeup, since it's easier to experiment with lipstick and shadow on a weekly basis. And when you get to the point that you just have to color your coif, take this advice from Pantene celebrity colorist Rita Hazan.

* Be a smart blond. Bleach is the most damaging and drying ingredient. It's okay to hit the bottle once every six weeks if you're only brightening up a shade or two. If you want to be lighter than that, use a bleaching kit once a month, going one level blonder each time until you reach your desired hue.