The distinctive smell of blood is due to the presence of iron in hemoglobin. When blood exits the body and is exposed to air, the iron in hemoglobin oxidizes, resulting in a metallic odor typically described as “coppery.” This scent is familiar to many people from experiences like minor cuts, nosebleeds, and metallic tastes in the mouth from blood. While not inherently dangerous, the smell of blood can cause unease due to cultural associations with injury, violence, and death. Understanding the science behind this smell may help demystify it.
What Causes the Smell of Blood?
Blood consists of red blood cells, white blood cells, platelets, and plasma. The red color and much of the smell of blood comes from hemoglobin, the protein in red blood cells that carries oxygen throughout the body. Hemoglobin contains iron, which gives blood its red pigment and metallic scent.
When blood remains inside the body, the iron in hemoglobin is in its reduced (Fe2+) state. This means the iron atom has donated two electrons and has a positive two charge. Upon exposure to oxygen in the air, the iron oxidizes to its ferric (Fe3+) state, gaining three positive charges by losing three electrons. This reaction happens quickly, causing the just-exposed blood to smell immediately.
The oxidation of iron in hemoglobin is accelerated by the copper atoms present in blood plasma. Copper acts as a catalyst for the reaction, facilitating the transfer of electrons from iron to oxygen. This interplay between iron and copper accounts for why the smell of blood is often described as “coppery.”
Why Do We Notice the Smell of Blood?
Humans have a remarkable sense of smell. We have about 6 million olfactory sensory neurons in the roof of the nasal cavity that detect airborne molecules. These sensory neurons contain receptor proteins that bind to specific molecules, sending signals to the olfactory bulb and brain.
The human nose can detect iron-laden blood even at very low concentrations. Some experts estimate humans can smell blood at concentrations as low as 1 part per trillion! At this level, only a few drops of blood are required to produce a noticeable scent.
This extreme sensitivity likely evolved in our primal ancestors, for whom an acute sense of smell was a critical survival tool. The ability to detect blood, whether from prey, predators, or tribe members, carried important information about food sources and threats in the environment. So while the smell of blood today may trigger unease, it once served the vital purpose of alerting our ancestors to signs of danger, food, and other critical information for survival.
Descriptions of the Blood Smell
Given the primal nature of the human sensitivity to it, it’s not surprising the smell of blood evokes visceral reactions and descriptions:
– Metallic – The iron in hemoglobin produces a scent similar to iron metals. Blood smells much like a penny or some other copper coin.
– Tangy – Blood has a tart, strong flavor that comes through in the aroma. The tang speaks to the rich mixture of proteins and minerals present.
– Warm – Since blood exits the body near body temperature, its smell often includes a sense of warmth. This contrasts with the cool smell of metals and contributes to the unique scent.
– Sweet – At high concentrations, blood has a subtly sweet, meaty aroma. The sweetness likely comes from organic molecules besides proteins.
– Sickening – While slight at low concentrations, at high concentrations, the odor of blood can be noxious and disturbing. The association with injury likely contributes.
– Rich – Blood’s complex blend of mineral and organic molecules produces a full sensory experience. The complexity led cultures like the Aztecs to view blood as life-giving and precious.
So while the smell of blood has nuance, the dominant metallic tang comes from the distinctive presence of iron-laden hemoglobin molecules.
Blood Scent Throughout History
Given its primal nature and associations, it’s fascinating to track how the smell of blood has woven through art, culture, and history:
Mythology
The metallic tang of blood permeates mythology and folklore. Chinese mythology describes “the smell of blood on the ground for 90 li,” conveying a senseless massacre. The nose of the Aztec god Tezcatlipoca is said to smell blood from a great distance. Vampire mythology claims the creatures smell blood and can differentiate people by its scent. Such myths underscore the scent’s primal nature.
Wars and Battles
The smell of blood was likely ubiquitous on ancient battlefields where death from blunt force trauma prevailed. Even into the era of guns and artillery, up through the World Wars, the smell remained present where carnage unfolded. Nurses and doctors had to grow accustomed to the scent to function and save lives. The overwhelming odor connects the smell of blood firmly to mortality.
Medicine
Before modern sterilization and antibiotics, there was no way to avoid the smell of blood in medical practice. Barbers pulled teeth and performed amputations. Bloodletting was used as a misguided medical treatment. As late as the American Civil War, the smell permeated military hospitals and tents for the wounded. While medicine is much less bloody today, for centuries the smell was central to the healer’s art.
Rituals
Some rituals and practices involve the smell and presence of blood. The Christian ritual of the Eucharist represents Christ’s blood using wine. Some Hindu rituals involve presenting blood offerings to deities. In parts of Africa, Maasai warriors drink blood during initiation. While such rituals make some squeamish today, they echo times when blood’s smell connected it to the divine.
Criminal Justice
With forensic science and DNA testing, blood analysis plays an important role in linking suspects to violent crimes. Detectives look for visible pools and droplets. They use chemicals to illuminate hidden traces of hemoglobin from attempts to clean up the scene of a crime. The connection between blood’s unmistakable essence and acts of violence continues today.
So while today associated with injury and danger, the smell of blood has influenced culture and society through the ages in diverse ways.
Why Does Blood Smell Repulsive Sometimes?
At low concentrations, blood’s odor provides humans with useful sensory information and cues. But at high concentrations, the smell becomes overpowering and can induce disgust or nausea.
There are several factors that make the smell of blood aversive or repulsive in certain contexts:
– Association with injury, pain, and danger
– Connection to death and mortality
– Presence of disease or pathogens
– Extreme intensity at high concentrations
– Rotten aroma from decomposition
– Induced nausea and vomiting
In terms of biology, smelling blood does not always mean one is in danger. But our instincts still associate the smell with potential threats to avoid. This conditioned response protected ancestors who reacted quickly to the slightest hint of blood.
Blood’s thick, sticky texture also heightens its disgust factor. The appearance enhances the noxious sensation of the smell. Blood is meant to stay inside the body, so its external presence provokes a deliberate repulsion to expel it.
Finally, the presence of vomit, feces, and infection in some wounds adds a putrid, rotten dimension to blood’s aroma. This goes against the brain’s deeply ingrained drive to avoid pathogens, decay, and filth.
So while useful at low levels, at higher concentrations, blood smells repulsive in order to keep us safe by promoting avoidance and spurring protective actions. But the aroma alone does not necessarily signal immediate peril.
Professions With Regular Exposure to Blood Smells
Due to the primal nature of blood scents, only certain professions come into regular contact with the smell as part of their work:
Doctors and Nurses
These front-line healthcare workers routinely see and smell open wounds, blood draws, surgeries, and other procedures. Dealing with the metallic scent of blood is a standard part of the job.
First Responders
Paramedics, firefighters, and EMTs often encounter bleeding victims at traumatic injury scenes with significant blood loss. Repeated exposure helps them act effectively to save lives.
Police Officers
At violent crime scenes, blood spatters, pools, and bloody weapons create smells police must contend with to assess evidence and preserve the scene.
Crime Scene Cleaners
These specialists clean up scenes after murders or suicides. They use chemicals and sanitizers to remove traces of blood and associated fluids.
Soldiers/Surgeons
On battlefields and in field hospitals, these professions dealt with horrific blood loss from past war injuries like amputations or gaping wounds.
Forensic Scientists
Analyzing blood patterns, DNA, and other markers involves getting samples up close. The needed detachment can take time to develop.
Veterinarians
Pets bleed from injuries, accidents, and surgeries. Vets require nose blindness to properly diagnosis and treat familiar household animals.
Regular exposure enables these professionals to perform their duties effectively without being distracted or repulsed. But it takes time to adjust through repeated contact with the heavy smell.
Cultural References to Blood’s Scent
Let’s explore some memorable cultural references that creatively captured the essence and impact of blood’s smell:
Shakespeare
“I have almost forgot the smell of fears.” Macbeth highlights blood’s scent as a primal reminder of mortal terror.
Hemingway
“There was a great splashing of blood.” Hemingway’s visceral style captures blood’s sticky presence.
Dracula
“…the sickly odour of blood was in the air.” Bram Stoker equates blood’s scent with the deadly vampire.
Carrie
“The smell is everywhere…a copper smell like pennies on the tongue.” Stephen King links blood to Carrie’s chaotic telekinetic fury.
The Shining
“His own blood rose around him in a gigantic cloud.” Stanley Kubrick films blood with dreamlike menace.
Great writers recognize blood’s smell taps into primal human responses, eliciting visceral reactions in readers. The scent makes tangible life’s fragility in ways words alone cannot always convey.
Conclusion
The distinctive scent of blood stems from iron-laden hemoglobin exiting the body. Though repellent in large amounts, at trace levels the smell served our ancestors and still warns us today of threats and opportunities for survival. While blood smells can provoke unease, their presence in our culture reminds us of life’s constant fragile balance. And for professionals like doctors, nurses, and first responders, the scent remains part of their heroic efforts to rescue others from dire fates. So while the blood smell touches our primal nerves, it also carries connotations of empathy, care, and our shared bonds in preserving life when possible.