After death, the body undergoes an inevitable process known as decomposition. This complex breakdown of organic matter is a significant focus within forensic science. Understanding its mechanisms and progression provides insights into the post-mortem interval and various environmental influences.
Early Post-Mortem Changes and Initial Odor
Decomposition begins immediately after death with internal changes. Without blood circulation and oxygen, cells break down through autolysis, or self-digestion. Concurrently, bacteria, particularly those in the intestines, become highly active and multiply.
These bacterial actions initiate putrefaction, generating distinct odors. A detectable decomposition smell typically begins within 24 to 48 hours. In very warm conditions, subtle smells might emerge within 10 to 12 hours, though it can take up to three days for the odor to become pronounced.
The Molecules of Decomposition
The intense smell of a decomposing body results from various chemical compounds. These are primarily volatile organic compounds (VOCs) released as anaerobic bacteria break down organic matter.
Putrescine and cadaverine are largely responsible for the foul, rotting flesh scent. Other notable odorants include skatole and indole, which contribute fecal-like smells.
Sulfur-containing compounds are significant, such as hydrogen sulfide (rotten egg smell) and methanethiol (rotting cabbage). Dimethyl disulfide and dimethyl trisulfide produce garlic-like or foul odors.
Influences on Decomposition Rate
The timeline for odor onset and decomposition varies significantly due to several influencing factors.
Environmental Factors
Temperature plays a substantial role; warmer conditions accelerate decay by increasing bacterial and enzyme activity. Colder temperatures slow the process, and freezing can halt it entirely.
The environment also impacts the rate. Bodies exposed to air decompose faster than those in water, where cooler temperatures and lower oxygen levels retard the process.
Burial slows decomposition by limiting insect access and airflow, with soil type and moisture content further influencing the rate. High humidity speeds decay, while very low humidity can lead to mummification.
Insects, particularly flies, arrive quickly and their larval activity accelerates tissue consumption.
Intrinsic and External Factors
Intrinsic factors like body size, fat content, and cause of death also affect progression. Embalming, a process involving preservative chemicals, can significantly delay but not entirely stop decomposition.
Evolving Odors Through Decay Stages
The smell of a decomposing body changes as it advances through distinct stages. During the initial “fresh” stage (up to two days), odors are minimal as autolysis begins.
The “bloat” stage (3 to 5 days) sees gases accumulate, causing the body to swell and release intense, gassy odors.
In “active decay” (5 to 11 days), tissues liquefy, and there is substantial loss of body mass. This stage is characterized by very strong putrefaction smells as bacteria and insects rapidly break down soft tissues.
In “advanced decay” (10 to 30 days), the rate slows, and odors become less intense as soft tissue is consumed.
Finally, during “dry decay” or “skeletonization,” most soft tissues are gone, leaving skeletal remains, and odors diminish significantly.