"OMG PU." That pithy review of CK IN2U Her provides as good an introduction as any to the hard-nosed approach to scent that authors Luca Turin and Tania Sanchez take in their new book, "Perfumes: The Guide" (Penguin). What with all the marketing flimflammery that accompanies each new fragrance launch, a map to the industry's wares was long overdue, and "Perfumes" fills the void capably. Along with being witty and knowledgeable about the chemistry and culture of perfume, Sanchez and Turin are whizzes at conveying, through words, all that the nose knows. This is no challenge to be sniffed at; after all, a great perfume (as Turin writes of Habit Rouge, by Guerlain) is "a bit like beauty itself—immediately understood, never quite elucidated." Where Turin and Sanchez are most insightful, however, is in their analyses of the mediocre scents that comprise the vast majority of the perfume marketplace. Anyone wondering if that pretty thing sprayed on her at Bloomingdale's will wear out its welcome sooner rather than later will find her answer here, along with several sensible hints about why you like the perfumes you like, and a few unprejudiced suggestions of scents that might have flown under the radar: Elternhaus' MoslBuddJewChristHinDao, for example, which according to Turin earns its five-star rating and "masterpiece" description by leaving the b.s. at the bottle stop.