“Strictly speaking, smells exist only in our heads,” writes psychologist and smell expert Avery Gilbert. “Molecules exist in the air, but we can only register some of them as ‘smells.’” It is impossible even to count how many scents there are. Yet the same chemicals turn up over and over again: The molecule MMP is the key aroma in green tea, grapefruit, basil, and cabernet sauvignon wine; dimethyl sulfide shows up in oysters, tomato paste, “spoiled refrigerated chicken, and pinto-bean farts.”
Gilbert covers areas from scent branding—even Samsung’s flagship store has a signature perfume—to how to sniff. And he offers an explanation for why Freud dismissed smell as an unimportant, vestigial sense. “The repeated insults of cocaine, nose surgery, influenza, sinus infection, cigar smoking, and finally aging left him with a clinically impaired sense of smell,” Gilbert writes. At least Freud didn’t have cacosmia, a medical condition that can make everything smell like, well, feces.