It’s well accepted now that we, humans and many other species, communicate by the sense of smell. There’s no language involved, except in the broadest sense. We can talk about the language of smell in an abstract way, but a linguist wouldn’t call it that. They wouldn’t find the identifiable structures, like word ordering and syntax, that a real language needs. For the rest of us, who aren’t sure what “syntax” means, really, the metaphor of language can be fitted quite comfortably to smell-based communication. We release chemical odors which represent our current mood and condition, they are detected by others who interpret what it means. Like all good communication, it’s two-way. People may release odors in return. Bursts of human smells might sweep the room in waves when people are together. Is it any wonder that the dog wants to be there?
Communication by smell is largely unconscious. We don’t notice most of it at a conscious level. We react to it reflexively, as the emotional center of the brain, smell’s first stop, deals with the details. As a result, our responses to different chemical cues happen before we know it. A return smell or a subtle change in facial expression, posture or tone of voice betrays our feelings. If we smell fear, anxiety, aggression or illness our bodies respond to it, showing any apprehension we might feel. As with smell, our faces, bodies and voices transmit meaning below the conscious level, so the conversation could be over before the first sentence is completed.
The chemicals used in communication, usually between members of the same species, include a subset called pheromones. They are known to influence and regulate behavior between individuals, especially among insects. Accepted as crucial to insects, pheromones have less and less support as we approach the human branch on the tree of life. Some scientists flatly reject any role for pheromones in human behavior. Others are only reluctant to say that we have pheromones specific to sex. As yet, no pheromone has been found in any published, peer-reviewed experiment to unambiguously stimulate human sexual behavior.
Are humans immune to the effects of pheromones, or are we simply reluctant to be lumped with other animals? A number of studies seem to suggest that odors play a role in human biology, from the synchronization of the menstrual cycle to a tendency to select mates whose immune systems differ from our own. It remains to be seen how much else we do based on what we smell.