See What I’m Saying:

The Extraordinary Powers of our Five Senses


Chapter 4: Like Marvin Gaye For Your Nose


Research suggests that humans can unconsciously smell each other's fertility, mood, and genetic compatibility.


        The recent smell research suggests that you are being effected by odors you never notice–possibly more often, and more strongly, than by the ones you do. Your everyday experience is that your nose spends much of its time ‘on-hold’ waiting for the next novel odor to waft by. When entering a new environment you do notice new odors, but once habituated, your nose seems to be at rest. Unlike your eyes and ears which always seem to be detecting something, much of your waking time seems scentless.

        But new research suggests that conscious smelling is just a very small fraction of what your nose does. Your nose is likely using odors all of the time, mostly in ways that don’t reach your consciousness. New research in physiology and neuropsychology reveals an olfactory system that is especially suited to subliminal input and processes. What’s meant by subliminal here (and by smell researchers), is simply when an odor is too weak to reach the threshold of your conscious awareness: it is unnoticeable. Importantly, subliminal does not imply coercion or manipulation of any kind.

        Despite the fact that they are too weak to be noticed, subliminal odors activate the nerve cells in your nose and induce activity in brain regions associated with your attention, memory, and emotion. This activation is similar to that initiated by consciously detectable odors. Even when you do consciously notice an odor, unconscious odors still influence your brain. In fact, by the time you notice a smell, your brain had already been activated by the smell a half second earlier: a lag that is much longer than for any of your other senses. And even after the odor reaches your consciousness, activity in regions specifically involved with subconscious odor processing continues to run in parallel with conscious odor brain processes.

        This new evidence has led a number of researchers to believe that much of your olfactory processing occurs on stimuli that never reach your awareness. And this hidden olfactory world can have subtle effects on your thoughts, preferences, and to some degree, your behaviors.

        For example, you would more quickly recognize cleaning-related words (“hygiene”, “tidying”) on a computer screen if a low-level, subliminal cleanser odor were presented as you responded. Also, this subliminal cleanser odor could influence what you reportedly planned for your day. Subjects are much more likely to report plans for cleaning-related activities (straightening their rooms, washing their cars), in the presence of an undetectable cleanser odor. Finally, a subliminal cleanser odor can actually help you become more tidy. Subjects who are asked to eat a crumbly cracker perform three times as many cleaning actions (wiping crumbs from their desk and mouth) if they are first exposed to the subliminal cleanser odor.