Death is a universal part of life, but many of the biological processes surrounding it remain unfamiliar to most people. Throughout history, that uncertainty has contributed to beliefs that humans might possess an unexplained “sixth sense” for recognizing death or danger. Science has not established the existence of a supernatural ability to detect death. However, researchers have discovered something genuinely interesting: the human body and brain can respond to certain chemical signals associated with decomposition, sometimes without us consciously realizing what is influencing our behavior.
One substance that has attracted scientific attention is putrescine, a pungent chemical compound associated with the decomposition of organic tissue. After death, biological material undergoes numerous chemical and bacterial changes, producing many different compounds and characteristic odors. Putrescine is one component of that complicated process, rather than being the sole chemical responsible for the odor of decomposition. Researchers have investigated whether humans respond behaviorally when exposed to this particular substance.
In 2015, researchers Arnaud Wisman and Ilan Shrira published a peer-reviewed study in Frontiers in Psychology titled The Smell of Death: Evidence that Putrescine Elicits Threat Management Mechanisms. Wisman was affiliated with the University of Kent’s School of Psychology, while Shrira was affiliated with Arkansas Tech University. Their research explored whether putrescine might function as a chemical warning signal capable of influencing human responses to potential threats.
The researchers were interested partly because chemical communication is widespread throughout the animal world. Animals use scents and other chemical signals for many purposes, including identifying food, finding mates and recognizing danger. Some species also demonstrate avoidance behavior when exposed to odors associated with dead members of their species. Avoiding decomposing material could potentially have survival benefits because it may reduce exposure to pathogens or other environmental hazards.
Wisman and Shrira wondered whether humans might retain comparable mechanisms. Instead of asking whether people could consciously recognize the smell of decomposition, they investigated whether exposure to putrescine could produce measurable changes in behavior. Their work consisted of four experiments examining reactions including vigilance, walking speed, threat-related thinking and defensive responses. The participants were exposed to controlled scent conditions rather than actual human remains.
In the first experiment, researchers investigated whether putrescine affected vigilance. Participants completed a reaction-time task after being exposed to different odor conditions. According to the published results, participants exposed to putrescine showed evidence of greater vigilance. The researchers interpreted this as consistent with the idea that the chemical could activate psychological processes involved in detecting possible threats in the surrounding environment.
This finding should not be interpreted as evidence that participants consciously believed someone had died nearby. That was not what the experiment demonstrated. Instead, it suggested that exposure to a particular chemical associated with decomposition could influence how alert people became. The distinction is important because popular descriptions of scientific studies can sometimes turn a subtle behavioral effect into a much broader claim than the evidence actually supports.
Another experiment examined avoidance behavior. Participants encountered putrescine, ammonia or a neutral scent condition before leaving the experimental location. Researchers then measured how quickly participants walked away. The study reported that people exposed to putrescine tended to move away more quickly than those in the comparison conditions. The authors interpreted this faster walking speed as behavior consistent with an avoidance response.
A further experiment examined both physical movement and psychological responses. Again, participants exposed to putrescine moved away more quickly, while researchers also observed greater accessibility of concepts associated with escape and threat. Together, these results supported the researchers’ hypothesis that putrescine might act as a chemosensory signal capable of activating threat-management mechanisms.
Perhaps one of the most interesting parts of the research concerned conscious awareness. In another experiment, the amount of putrescine used was sufficiently subtle that participants did not report noticing the odor during the subsequent debriefing. Even under those conditions, the researchers reported behavioral differences consistent with increased defensive readiness. This suggested that chemical information might influence certain responses without people consciously identifying the scent responsible.
The findings fit into a larger area of research examining how smell influences human psychology. People do not always consciously recognize the many ways odors affect emotions, memories, preferences and behavior. A familiar scent can suddenly bring back an old memory, while an unpleasant odor can encourage someone to leave an area before they have consciously considered why. Human olfaction therefore involves more than simply deciding whether something smells pleasant or unpleasant.
Putrescine is especially interesting because of what it represents biologically. The substance is associated with decaying tissue, meaning that detecting and avoiding it could potentially have provided advantages during human evolution. Decomposing organic material can be associated with biological hazards. In natural environments, dead animals may also sometimes indicate predators or other threats. A tendency to become more alert or move away from certain decomposition-related signals could therefore potentially be useful.
However, the researchers did not establish exactly why humans respond to putrescine in this way. Behavioral reactions to smells can arise from evolutionary mechanisms, learned experiences or combinations of the two. Additional research would be needed to determine precisely how these processes interact. Scientific caution is particularly important here because demonstrating a behavioral response in controlled experiments does not automatically explain every reaction humans might have to similar odors in everyday life.
It is also inaccurate to claim that putrescine allows people to predict when another person is going to die. The experiments did not test such an ability and provided no evidence that humans can smell an approaching death before it occurs. Putrescine is associated with biological decomposition, which is fundamentally different from predicting death in a living individual. Descriptions claiming that humans can literally “smell death coming” therefore go beyond the evidence presented by the researchers.
Similarly, the findings should not be described as scientific confirmation of a supernatural “sixth sense.” Smell is one of the established human senses, and unconscious processing of sensory information is a normal biological phenomenon. Our brains continually process information that does not necessarily become part of our immediate conscious awareness. The putrescine experiments are interesting precisely because they may demonstrate how an ordinary sensory system can influence behavior in surprisingly subtle ways.
Another misconception worth avoiding is the idea that putrescine alone creates the characteristic odor associated with decomposition. Decomposition involves numerous chemical compounds produced as biological tissue changes. Putrescine is one of those substances, alongside other compounds. The phrase “smell of death” is memorable and was even used in the title of the scientific paper, but the chemistry of decomposition is considerably more complicated than a single molecule.
The study’s results nevertheless provide intriguing evidence about the relationship between smell and human defensive behavior. Across several experiments, exposure to putrescine was associated with responses such as increased vigilance and faster movement away from an area. The researchers interpreted the overall pattern as support for the idea that humans possess mechanisms capable of responding to chemical signals associated with potential environmental threats.
These findings also demonstrate why the human sense of smell should not be underestimated. Vision and hearing often receive the most attention when people discuss how humans identify danger. Yet smell provides important information as well. The odor of smoke can warn of fire, spoiled food can signal that something should not be eaten, and other environmental odors can influence whether we approach or avoid particular surroundings.
What makes olfaction especially fascinating is that some of its effects can occur without deliberate thought. Someone may become uncomfortable in an environment before consciously identifying an unpleasant smell. This does not necessarily mean that a mysterious sense is operating. Instead, the nervous system may simply be processing sensory information more quickly or subtly than conscious awareness allows us to recognize.
Research such as Wisman and Shrira’s helps scientists investigate those mechanisms under controlled conditions. Rather than relying on anecdotes about people supposedly sensing death, researchers can expose participants to specific chemicals, compare their responses with control conditions and measure behavioral changes. This approach allows extraordinary claims to be separated from effects that can actually be observed and tested.
The study also illustrates why scientific findings sometimes become exaggerated when they spread online. Saying that researchers found behavioral responses to putrescine is accurate. Saying that scientists proved humans possess a hidden ability to know when death is nearby would be misleading. Maintaining that distinction makes the underlying discovery no less interesting—in fact, the real biology may be more fascinating than the exaggerated version.
Human beings constantly interact with an environment filled with sensory information. Much of it receives conscious attention, but some appears to influence us more subtly. Putrescine offers researchers one possible window into how ancient threat-detection mechanisms may operate through smell. The evidence suggests that exposure can affect certain behaviors under experimental conditions, although many questions remain about the mechanisms and their significance outside the laboratory.
Death itself continues to involve profound biological, philosophical and emotional questions, many of which science cannot reduce to a single explanation. What research can do is examine individual processes carefully and determine which claims are supported by evidence. In this case, scientists have not discovered a supernatural ability to sense death. They have found evidence that a chemical associated with decomposition can influence human threat-related responses.
That conclusion may be less sensational than saying humans can “smell death,” but it is scientifically much more meaningful. Our noses and brains constantly collect information about the world, and some of those signals may influence our behavior before we consciously recognize them. Research into putrescine provides a fascinating example of just how complex that relationship between chemistry, perception and human behavior can be.
