If your hair flows below your shoulders, it's only a matter of time before split ends pop up. At a certain point, months (or years!) of heat styling tend to leave the ends looking rough and ragged. Enter Kerastase's Cristalliste Lumiere Liquide ($42), an incredibly light hair serum designed for long locks. The featherweight formula doesn't weigh strands down, and if you like floral scents, you'll appreciate the light perfume effect. Add a few drops to dry hair, and you'll be rewarded with sleek, shiny strands — and unruly ends are immediately tamed. Talk about a smooth move.