What makes the finding striking is that people do not consciously register the smell as dangerous, nor do they associate it with death or fear. The reaction happens below the threshold of awareness — the brain processes the chemical signal and triggers a behavioral response before the conscious mind has any say in the matter.
Smell and survival: an ancient connection
The olfactory system is one of the oldest sensory systems in evolutionary terms, directly linked to brain regions that govern emotion and instinct. Research into chemical communication — including pheromones and decomposition compounds — has grown steadily as scientists seek to understand how much of human behavior is shaped by signals we never consciously register. Putrescine is a naturally occurring polyamine produced during the breakdown of organic matter.
Experiments show people move away — just like animals fleeing danger
In experiments conducted by Wisman and Shira, participants exposed to putrescine consistently moved away from the source of the odor. The researchers draw a direct parallel with animal behavior: across species, the detection of a decomposition signal prompts either flight or a defensive response as part of a core survival mechanism.
The two scientists argue that humans retain this same instinct. “It is hard to think of a scent as frightening,” other researchers in the field acknowledge — yet the behavioral data shows that scents do make people measurably more vigilant of their surroundings, even when they cannot identify what they are reacting to.
The opposite of attraction: how putrescine differs from sexual pheromones
To understand the significance of putrescine’s effect, Wisman and Shira place it in contrast with sexual pheromones — odors produced by males or females that stimulate behavioral reactions in the opposite sex and encourage proximity for mating purposes.
Where pheromones draw people together, putrescine pushes them apart. “Putrescine signals a different type of message than pheromones, but people’s responses to putrescine (avoidance and hostility) do seem indeed to be the opposite of responses to many sexual pheromones,” the researchers explain. Both types of chemical signal operate largely outside conscious awareness, yet each steers human behavior in a distinct direction.
As Wisman and Shira note: “We do not know why we like (or dislike) someone’s smell, and we’re usually not aware of how scent influences our emotions, preferences, and attitudes.” The research adds another layer to that puzzle, showing that the olfactory system is doing far more work than most people realize.
A survival reflex shared across species
The broader argument put forward by Wisman and Shira is evolutionary: the ability to detect chemical signals of danger — whether decomposition or a rival’s presence — is part of what has allowed species, including humans, to survive. Smell, in this framework, is not merely a sensory pleasure but an ancient warning system.
