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?