The smell of a deceased body is a complex and often unsettling topic, yet understanding this natural process is a part of forensic science and the broader study of biological cycles. Decomposition involves a series of chemical reactions and microbial activities that break down organic matter, leading to the release of distinct odors. This article aims to demystify the science behind these characteristic smells, exploring the specific compounds involved, how the odor changes over time, and the factors that influence its intensity and nature.
The Chemical Basis of Decomposition Odors
The distinct smell of decomposition arises from volatile organic compounds (VOCs) released as microorganisms break down tissues. Putrescine and cadaverine are prominent compounds, largely responsible for the “rotting flesh” or “rotting fish” smell. These diamines are byproducts of bacterial breakdown of amino acids.
Other contributors include skatole and indole, which produce a fecal or mothball-like scent. Skatole forms from tryptophan decomposition in the digestive tract, while indole also results from bacterial processes.
Sulfur-containing compounds also play a role. Hydrogen sulfide, known for its “rotten egg” smell, is produced when organic matter breaks down without oxygen. Mercaptans, or thiols, contribute sulfurous odors, with methanethiol smelling like rotten cabbage. Dimethyl disulfide and dimethyl trisulfide, smelling like foul garlic, are also present.
How the Smell Changes Over Time
Decomposition odors evolve through different stages of decay. In the initial “fresh” stage, lasting up to a few days, the odor is minimal, with few volatile organic compounds detected. Autolysis, the self-digestion of cells, begins, but putrid smells are not yet prominent.
As the body progresses into the “bloat” stage, within 3 to 7 days, bacterial activity intensifies, leading to gas production and swelling. This pressure forces fluids and gases out, making the stench apparent and causing the greatest odor during decay. The smell becomes more complex and intense during the “active decay” stage, beginning around 7 to 10 days postmortem. During this phase, bacteria proliferate, consuming soft tissues and releasing a wider range of VOCs.
In the “advanced decay” stage, from 25 to 50 days, most soft tissues have broken down, and the smell begins to diminish. Remaining odors might be more earthy or moldy, influenced by fungal activity. By the “skeletonization” stage, when most organic matter has decomposed, the associated odor becomes negligible or absent.
Influences on Decomposition Odor
Several factors can alter the intensity, type, and duration of decomposition odors. Environmental conditions play a role; higher temperatures and humidity accelerate microbial activity, leading to faster decomposition and more intense odors. Conversely, cooler temperatures slow the process. Air circulation also impacts odor dissipation, with limited airflow trapping smells and making them more potent.
Body location affects the odor profile; for example, buried bodies may differ from those exposed to air or water. Body composition, like fat content, can influence breakdown products, as can clothing or physical barriers. Factors like cause of death or trauma can provide entry points for bacteria, altering chemical reactions and odors. Insect and scavenger activity accelerates decomposition, changing the odor profile by consuming tissues and introducing new microbial communities.
Our Response to the Smell
Humans, along with many animals, exhibit an instinctive repulsion to the smell of decomposition. This aversion is a protective mechanism, signaling pathogens and associated dangers like disease. The distinctiveness of these odors makes them recognizable and often lingers in affected areas.
The smell of decomposition can evoke emotional and psychological reactions in humans, including distress, nausea, and revulsion. This visceral response is an innate instinct, contributing to our avoidance of decaying matter. Even at low concentrations, the “stench of death” can be perceived, triggering a negative reaction.