Those smarty-pants chemists and hairstylists at Living Proof have done it again, this time, with a leave-in treatment that both hydrates and soothes a dry, itchy scalp. The secret? A probiotic complex that promises to balance the levels of all the microorganisms on your scalp (both good and bad — hey, we all have them), plus hydrating hyaluronic acid. Also important: It's fast absorbing, and doesn't leave behind any residue.