We all know how distinct odors can enhance a scene. What does buttery popcorn evoke in you? What about freshly baked apples? Or steamed lobster? Or a campfire?
Those are all wonderful smells that make us feel happy, excited, or content. However, fiction shouldn’t only include pleasant or comforting scenes, or the narrative feels fake. Real life isn’t all rose petals (another great smell). So, why do some writers shy away from rank or offensive odors?
“Odors have a power of persuasion stronger than that of words, appearances, emotions or will.”
— Patrick Süskind, author of Perfume: The Story of a Murderer
I’m one of those strange people who love the smell of blood. When I read “a metallic” or “irony” stench, it doesn’t elicit a shocked or fearful response in me. You know what does elicit a visceral response? Stress sweat.
Stress sweat has a very distinctive smell, which only occurs during times of “flight or fight.”
I heard a reference to it recently in a movie. One character said to another, “Why does stress sweat stink worse than regular sweat?” And I thought, huh, they’re right. Why does it smell worse?
Down the research rabbit hole, I dove. What I discovered blew my mind. Now, I’m sharing it with you because, y’know, that’s what writers do. Perhaps you can use some of this research to add realism to your story.
Stress Sweat
Stress sweat has a unique pungent odor because it’s produced by the apocrine glands (located in the armpits and groin), rather than the standard eccrine glands used for heat regulation. Triggered by adrenaline, this sweat is thicker, milky, and rich in proteins and lipids (fats). Skin bacteria feed on these nutrients, and produce volatile, odorous compounds.
The Science of Sweat
When we are hot or exercising, our body uses eccrine glands to cool down. This sweat is 99% water and salt, with almost no odor. However, psychological stress triggers our “fight or flight” response, which releases hormones like adrenaline and cortisol. These hormones activate the apocrine glands, located in areas with high concentrations of hair follicles, like underarms and groin.
The resulting stress sweat stands out due to the following reasons:
- Nutrient-Rich Fluid: Unlike watery exercise sweat, apocrine glands secrete a thick, milky fluid packed with proteins, lipids (fats), and fatty acids.
- The Bacterial Feast: The bacteria naturally living on your skin thrive on these fats and proteins. As the bacteria consume and break down these nutrients, they produce volatile organic compounds that emit a sharp, foul odor.
- Massive Volume Increase: When our body enters “fight or flight” mode, our underarms can secrete roughly 30 times more sweat than when we are at rest. This creates excess food for the bacteria, which intensifies a sudden concentration of body odor.
Several factors, including sex, genetics, age, and diet can influence the type of odor that an individual emits. In fact, it has been suggested that, like a fingerprint, every individual’s body odor is unique and may be partly determined by genetics.
Ever lost a loved one and clung to their pillow, hoping and praying their scent would never fade?
Men have larger sweat glands and generally produce more sweat than women.
Fun Fact: Deodorants contain chemicals that kill skin flora and block production of stinky byproducts. Antiperspirants reduce the amount of sweat by clogging sweat glands. Many contain aluminum chloride, which creates a gel-like substance that forms a plug at the sweat ducts in the skin.
Biological Triggers for Other Offensive Body Odors
Sickness/Infection Odor (Volatile Organic Compounds)
Diseases change body chemistry. Diabetic ketoacidosis smells like rotting apples. Liver failure smells musty or fishy. Infected wounds smell sweet and sickeningly fruity due to specific bacteria. For some reason, I can detect the infection smell quite early. Not sure why I’m sensitive to it, but I’ve helped more than one animal before the infection spread enough to be noticeable. Maybe that’s my superpower. 🙂
In early stages, humans cannot detect the smell of cancer, but dogs can…
Dogs have up to 300 million scent receptors compared to humans’ 5 or 6 million, allowing them to detect scents in parts per trillion. They detect cancer by smelling specific Volatile Organic Compounds (VOCs) released by bodily tissues when cancer alters the body’s metabolism and cellular chemistry.
Often, what people detect as a “cancer smell” is actually a side effect of chemotherapy. Patients receiving treatment may excrete chemical byproducts through their skin and fluids, leading to odors described as metallic, like burnt hair, or like ammonia/chlorine.
Starvation/Dehydration Breath (Ketones & Decreased Saliva)
When someone’s saliva dries up, anaerobic bacteria multiply, causing a dead, sulfurous breath. If they enter starvation, their body burns fat for fuel. This creates chemical or metallic acetone breath.
Plants & Animals
Flowers produce fragrances as an evolutionary strategy to attract pollinators and ensure reproduction, and many species of insects, fish, and mammals emit peculiar odors to attract mates. In fact, male brown lemmings can tell whether a female has ever mated simply by her odor.
The Evolutionary Purpose
Scientists believe stress sweat served an evolutionary function. In early human history, stress sweat acted as a chemo-signal to warn others of danger. Studies have shown when humans smell the stress sweat of others, their brains automatically become more alert and are more likely to perceive neutral cues as potential threats.
Chemical Signaling (Olfactory Communication)
Humans evolved to unconsciously detect the chemical composition of fear and anxiety. When others detect these specific odors, it triggers increased alertness and vigilance in their own brains, warning them of unseen dangers.
Enhanced Grip for Survival
Sweating on the palms and soles is an evolutionary adaptation intended to dampen the skin, which improves friction and grip when we need to run, climb, or fight for our lives.
Predator Deterrence
Some evolutionary biologists theorize that putting off a sharp, unappealing scent when terrified may have helped startle or deter predators evaluating the vulnerability of prey.
I found more information on how the aging body’s chemistry changes (i.e., the smell of nursing homes), but I had to stop before this post turned into a book.
For fun, what’s your favorite smell? What smell churns your stomach acids? Are there any smells you’re overly sensitive to?
Forensic science is always evolving to better aid in the apprehension of criminals. What if a killer leaves his victim with no fingertips, DNA, or teeth? One way to determine the age of a victim is by examining their eyes.



This little guy is very much alive. Look how convincing he is, though!
Texas indigo snakes—a subspecies of the eastern indigo snake—can grow up to 7 feet long and are found throughout Texas. They’re not venomous, nor constrictors. Instead, they rely on muscular jaws to overpower and swallow their meals head first. Texas indigo snakes even hunt venomous rattlesnakes (they’re immune to the venom).
documented 29 out of 50 different wild ducks played dead when exposed to captive red foxes. This immediate collapse gives the duck a fighting chance should the fox lower its guard. The ducks remained still while the fox carried them back to den to escape later.
Another species of bird that plays dead is the Japanese quail. These animals do so for similar reasons to ducks – to avoid predators, such as cats — and wait for an opportunity to escape. When sleeping, Japanese quail also appear to be dead and can sometimes cause alarm to their owners.
The lemon shark is an apex predator, yet they also play dead. If turned onto its back, the lemon shark will not only play possum, they’ll begin to exhibit labored breathing and the occasional tremor. This is especially interesting, considering the lemon shark lay on the ocean floor and allows other animals to pick the parasites off its body. They have the ability to remain completely still and pump water over their gills to breathe.
This little guy is alive, playing dead.
Native to Japan, the pygmy grasshopper displays a unique version of playing dead when threatened. Not only do they freeze but they spread out stiffened legs as far as possible in all directions. This death stance makes it nearly impossible for predatory frogs to attempt to swallow them. Thus, the frog moves on to easier prey.
This redback spider is alive but playing dead.
And the acting award goes to…
The Central American cichlid plays dead to lure unsuspecting prey. This aquatic predator’s intricate markings give the illusion of a decaying fish. Because scavengers are attracted to an easy meal, they move in. The cichlid springs to life and attacks.
Another animal that plays dead to catch prey is the pselaphinae beetle. Instead of waiting in ambush, these beetles employ tonic immobility so ants can carry them away. Once they get inside an ant’s nest, they spring to life and feed on the ant larvae (the majority of their diet).
Black widows are the most venomous spiders in North America, but they don’t always bite when threatened or provoked. Instead, black widows often play dead. When their lives are at risk, they curl into a ball while releasing silk to aid its movement.
Blue Jays play dead by slumping down, motionless. Sometimes, like their crow cousins, they’ll sprawl out with their wings spread, head flopped to the side. Some birdwatchers theorize this is a form of blue jay sunbathing. Or they’re playing a practical joke since they often surprise people by springing to life if disturbed. When threatened by predators such as cats and hawks, they will absolutely play dead.
Praying mantis are easily recognized by their long narrow bodies, a small head with large eyes, and oversized front legs held upright. To avoid being eaten by the female after mating, the male will play dead. They will only move again once the female has lost interest and left.
Not to worry. She’s alive, just not in the mood.
Thank you for standing in for the human, sweet puppy.

Becca Puglisi