Scent of survival: How the smell of death drives our instincts

Putrescine is an organic chemical compound resulting from the decomposition of animal and human tissues. It is responsible for the characteristic odour of rotting meat, often described as the "smell of death."

At first glance, putrescine might seem insignificant beyond its repulsive smell, but scientists have discovered that its impact goes much deeper — reaching into our subconscious.

In 2015, a research team decided to examine how putrescine affects human behaviour. The experiments aimed to determine whether this scent could be perceived as a danger signal and how it influences our defensive reactions.

The results were surprising: even short-term exposure to putrescine heightened alertness and triggered defence mechanisms, such as readiness to flee or even aggressive behaviour. Importantly, study participants did not need to consciously smell it for their brains to react to its presence.

Several experiments were conducted to better understand how putrescine works. In one, participants' reactions to different scents were studied: putrescine, ammonia, and water. The results showed that those exposed to putrescine were more alert and responded quicker to stimuli than individuals in the control group.

Another experiment focused on escape-related behaviour. Participants pre-exposed to the smell of putrescine moved faster, suggesting that the compound triggered a subconscious sense of danger. Yet another experiment examined putrescine's impact on thinking. Participants completed language tasks and then had to walk a certain distance. Those exposed to the compound moved faster and were more likely to choose solutions related to threat concepts.

One of the most interesting aspects of these studies was that putrescine is effective even when not consciously perceived. In one experiment, participants exposed to low concentrations of the compound became more hostile toward an author of a critical essay against Western values, suggesting that the scent triggers defensive reactions on a deep, subconscious level.

Putrescine acts as a danger signal, potentially triggering fight-or-flight responses. This mechanism has evolutionary roots — for our ancestors, detecting the smell of a decomposing body could signify imminent danger, such as predators or diseases. Quick reaction to such signals could determine survival.

These reactions occur at a subconscious level, which shows how strongly our brains are wired to detect potential threats. Minimal signals, such as a faint smell of putrescine, can trigger responses that helped our ancestors survive in a hostile environment.

Putrescine is just one of many chemical compounds that influence our behaviour. Another well-known example is pheromones, which play a key role in communication between organisms, especially in the context of reproduction. Pheromones can affect mood, stress levels, and even mate selection.

Equally interesting is a chemical compound called geosmin, which is responsible for the smell of earth after rain. Although many people find this scent pleasant, scientists have discovered that its role in nature is much more practical — geosmin signals the presence of a moist environment, which could have been crucial for the survival of humans and animals in the past.

Research on putrescine and its impact on human behaviour opens new directions in exploring how scents affect our emotions and reactions. Our sense of smell might be much more connected to our evolution than we might have assumed.

Although seemingly distant from our daily lives, the defence mechanisms triggered by the smell of death still affect us on a deep biological level. It's a reminder that even in today's world, our biology shapes many aspects of our lives in ways we are only beginning to understand.