The power of scent is getting a lot of ink lately. A study last year indicated that certain scents delivered 
during sleep help improve memory. A study earlier this year indicates that the aroma of cookies entices people to spend more money. And lo and behold, just recently we found out that merely the scent of coffee can calm nerves.
Scientific American has a quite good article that discusses the power of scent in all of its complexity. Here’s a brief “whiff” of a section of the article on unconscious identification by scent:
Although humans probably do not ordinarily use smell to navigate toward the nearest source of chocolate, we do seem to use odors—in most cases, subconsciously—to evaluate potential mates. Each of us has a unique scent: milky exudates of various glands, including the apocrine glands, which are located around the nipples, genitals and armpits, contain roughly 200 chemicals. The ratio of chemicals, which are metabolized into an aromatic brew by skin-dwelling bacteria, varies from person to person. Men and women, for example, have distinct odors governed by different ratios of sex hormones.
Neurons that convey odors from the nose to the brain’s olfactory bulb have close connections with the oldest areas of the human brain: the limbic system, the region that includes the amygdala, which governs emotions such as aggression and fear, and the hippocampus, which controls memory acquisition. Thus, odors trigger subconscious emotional responses before arriving at the brain’s outermost section, the cerebral cortex, for conscious assessment. What this means, Lundström explains, is that “a great deal of processing odor is done on a nonconscious basis.”
David DiSalvo is a writer and research wonk whose work appears in Scientific American Mind, True/Slant and a variety of other places. More info 
