Biological Responses to Fear

Last night, my husband and I went to a pumpkin festival with another couple. The town blocks off downtown’s main drag, and skeletons, witches, monsters, live music, and laser shows filled the streets.

Dozens of lit jack-o-lanterns on shelved staging fringed one side of the road — the focal point of the evening’s festivities. The only thing missing was a haunted house. Fine by us. We don’t chase the adrenaline high of fear.

Which brings me to today’s subject: Fear

Fear is a universal, physical response to danger. We associate fear as a negative emotion, but it also plays a vital role in keeping us safe by mobilizing us to cope with potential dangers.

What happens within the body when we’re fearful?

Fear begins in the amygdala, which then activates the pituitary gland, where the nervous system meets the endocrine (hormonal) system. The pituitary gland then secretes adrenocorticotropic hormone (ACTH) into the bloodstream.

Meanwhile, the sympathetic nervous system — a division of the nervous system responsible for the fight-or-flight response — nudges the adrenal gland, encouraging it to squirt  epinephrine (aka adrenaline) and other catecholamines into the bloodstream.

The body also releases cortisol in response to ACTH, which raises blood pressure, blood sugar, and white blood cells. Circulating cortisol turns fatty acids into energy for the muscles to use should the need arise.

Catecholamines include epinephrine and norepinephrine, both hormones that prepare the muscles for violence by causing the following:

  • Boost activity in the heart and lungs
  • Reduce activity in the stomach and intestines, producing “butterflies” in the belly.
  • Inhibit the production of tears and saliva, which explains why dry mouth often accompanies fright.
  • Dilate the pupils.
  • Produces tunnel vision.
  • Reduces hearing.

The hippocampus part of the brain is heavily involved in memory, whereas the prefrontal cortex aids in high-level decision making. Both these areas help us control the fear response and determine if the danger is real or exaggerated. If the latter, these areas of the brain dampen the fear, allowing us to read scary books or watch slasher films.

Biologically, fear responses include:

  • Increased breathing.
  • Increased heart rate.
  • Peripheral blood vessels in the skin constrict while central blood vessels around vital organs dilate and flood with oxygen and nutrients.
  • Blood pumps the muscles so they’re ready to react.
  • Muscles at the base of each hair tighten, causing piloerection aka goosebumps.
  • Eyebrows raise and pinch together.
  • Upper eyelid raises while the lower tenses.
  • Jaw may slack and part stretched lips.
  • Voice pitch rises, tone strains.
  • Posture either mobilizes or immobilizes or fluctuates between both.
  • Breath shallows.
  • Muscles tighten, especially in the limbs.
  • Increased sweating.

Metabolically, glucose levels spike to provide energy if needed for action. Fear also increases levels of calcium and white blood cells.

Tips to Show Fear

To show a believable fear response in your main character, consider the above scientific and biologic changes within the body. Then get creative. An effective way to enhance fear is to slow down. Visualize the context. What’s happening in this moment? What is the character experiencing, moment by moment? By drilling into slivers of time, we’re telling the reader to pay attention. We’re creating emotional resonance. We’re drawing readers farther into the story, forcing them to turn the page.

Trigger the Senses

Do shadows obscure the threat? (sight)

Do the leathery wings of a bat flap overhead? Or do footsteps ricochet off the building and make it difficult to pinpoint direction? (sound)

Does the metallic sweetness of blood assault the back of the throat? (taste) Or fill the sinuses? (smell)

Is the thick bark of the ash tree she’s hiding behind rough and scratchy? (touch)

We already know hearing is impaired by biological changes. How does the impairment affect the MC? Do muffled sound waves heighten other senses? Or does the MC enjoy the adrenaline rush that accompanies fear?

Emotion is Layered

Characters shouldn’t be totally fine one second then immediately immobilized by terror. Let emotions build over time, even second by second.

“In the real world, no two people are alike, which means each of us expresses emotion in our own way. Some people find it perfectly natural to share what they feel with those around them, experiencing little to no discomfort with their emotions being on display. Others find the idea of revealing what they feel horrifying and will avoid situations that could lead to such vulnerability. Most fall somewhere between these extremes. This spectrum of expressiveness is called an emotional range, and it will influence not only which feelings a person overtly shows but when and how they will manifest.”

—Angela Ackerman & Becca Puglisi, the Emotion Thesaurus

Emotions — especially ones as extreme and universal as fear — unfold on a continuum. To impact the reader, show the MC’s physical and emotional responses in the correct order and with the proper intensity, or fear may come across as irrational or melodramatic.

Any adrenaline junkies in our audience? Do you ride roller coasters? Like haunted houses? Have you ever zip-lined? What about jumping out of an aircraft? Care to share a frightful experience?



This entry was posted in #amwriting, #writetip, #writetips, Fear and tagged , , , , , , , by Sue Coletta. Bookmark the permalink.

About Sue Coletta

Sue Coletta is an award-winning crime writer and an active member of Mystery Writers of America, Sisters in Crime, and International Thriller Writers. Feedspot and named her Murder Blog as “Best 100 Crime Blogs on the Net.” She also blogs at the Kill Zone (Writer's Digest "101 Best Websites for Writers") and Writers Helping Writers. Sue lives with her husband in the Lakes Region of New Hampshire. Her backlist includes psychological thrillers, the Mayhem Series (books 1-3) and Grafton County Series, and true crime/narrative nonfiction. Now, she exclusively writes eco-thrillers, Mayhem Series (books 4-7 and continuing). Sue's appeared on the Emmy award-winning true crime series, Storm of Suspicion, and three episodes of A Time to Kill on Investigation Discovery. Learn more about Sue and her books at

39 thoughts on “Biological Responses to Fear

  1. Good drill down, Sue. In my workshops, when I talk about scene writing, I say Fear is the key. It’s a continuum, as you point out. From worry to outright terror. Every scene needs some aspect of fear in the viewpoint character or things are just not crucial enough.

    As for thrill seeking, in the words of Samuel Goldwyn, include me out. My daughter got the thrill gene through her mother. At Disneyland once they convinced me to try the Tower of Terror…that’s the ride with the elevator drop that feels like it starts two miles high. When the drop commences, a camera takes a souvenier photo. In that photo I’m in the middle with an Edvard Munch scream look on my face, as daughter and wife look at me, laughing.

    No thank you. I’ll take Mr. Toad’s Wild Ride instead.

    • Hahahaha. I can picture that photo, Jim. Hilarious! But I’m with you. My family couldn’t get me anywhere near rides of that nature. I like my feet on solid ground, thank you very much. 😉

  2. Roller coasters? Definitely – but the old school wooden ones that rattle and shake like they’re coming apart at every nail – the newer metal ones with loops and such go too fast, are over too soon for my taste…

    Haunted houses? Yes and no… I worked in the one at Six Flags here in Atlanta – pretty tame compared to these Halloween slasher houses set up just for the “holiday” – and saw all different reactions to some pretty cheesy, tame attempts at terror… just don’t touch me – or get close enough that I think you’re gonna…

    Jumping out of a perfectly good airplane? Not even remotely interested…

    • Two out of three is still impressive, George. LOL Agree about advancing or touching me in a haunted house. My first reaction is to defend myself, and that’ll ruin everyone’s night.

  3. Jump out of an airplane? ARE PEOPLE CRAZY? Or bungee jump? Uh, no thank you. Now haunted houses–I like that kind of fear. I know it’s not real.

    Ohhh. What about a story where someone works at a haunted house and she knows it’s not real but a murderer comes after her…

    Great’s this for fear: My deadline is looming, like now and the book isn’t finished. THAT fear will either kick you into gear or paralyze you..

  4. I don’t like jumping down from a 3 foot retaining wall. Don’t even like the sensations on swings. Feet planted firmly on the ground, thankyouverymuch.
    Although I did enjoy the Matterhorn because it was more curves than drops.

  5. Sue, I always learn from posts where you drill down into physiological responses. Never knew how/why goosebumps happen until I read your explanation. Thanks!

    Adrenaline junkie? Not this coward. Imagination provides all the excitement I want.

    Although skydiving does sound kinda fun cuz it’s like flying. But there’d better be a giant net to catch me before I hit the ground.

  6. Wonderful post. Kay. Great review of hormonal and neurological responses to fear. Thanks for referencing my article on the sense of smell.

    Isn’t it amazing how, here at the Kill Zone, many of us are not thrill junkies. Count me in with those who have confessed. There is enough danger, plenty of risks, to simply navigating our roads and crowded spaces. But give me a big tree that’s hung up in another tree (a widow maker), or branches of a tree that are tangled and just waiting to snap forward when freed, and I’m all in. It’s like a chess game where I have a fair chance, and the next move is mine.

    Have a calm and relaxing weekend!

    • That’s right, Kay. I remember that post. Excellent story!

      TKZers, if you haven’t read about Kay’s frightening run, check it out. Definitely a pulse pounder.

  7. All you who are near Disneyland… I’m jealous. I went last year, but the Matterhorn was closed, and so was the other rollercoaster in the other park.

    Excellent post, Sue. Though I didn’t understand half the medical jargon, the overall explanation makes sense. One question that occurred to me was what happens to a person when they’re constantly in a state of fear?

    Rollercoasters, yes unless they go upside down too sharply (I love the Batman ride at Six Flags, but Superman? Never!). And I have gone ziplining. Haunted houses, the one time I’ve been I was bored (maybe because most of the scares are visual? Not sure). Jumping out of an airplane would be fun if it didn’t require so much planning and prep, but I’d go hang gliding any day.

    • Great question, Azali!
      A prolonged sense of fear can have many negative effects on the body, including:
      * Physical health problems can develop
      * Fear weakens the immune system
      *Can cause cardiovascular damage
      *Gastrointestinal problems, such as ulcers and irritable bowel syndrome
      *Decreased fertility

      Humans weren’t built to stay in a frazzled state. Hence why chronic fear does so much damage.

      Good point about only visual scares lessen the fear factor… in writing and in life.

  8. Fantastic post, Sue. Your deep dive into fear is a keeper. RE: physical response. Sometimes it’s been butterflies, other times I’d describe my stomach as knotted or even roiled in response to fear. However, the roiled comes *after* the situation which created the fear.

    I’m not a thrill seeker. No sky diving, zip lining, or bungee jumping for me. I don’t even want to clamper onto our roof. I’m usually good for one or two serious thrill rides in Disneyland, otherwise, I like it thrill free.

    The thrills I seek are related to awe, like the Hunter’s Moon Saturday night, rising brilliant and huge in the eastern sky. I tagged you on “X” with a Moon pic 🙂

    Have a wonderful week!

  9. Great post, Sue!

    I also didn’t know about those tiny muscles at the base of each hair…

    When my kids were . . . kids, we lived in S. CA. My bro-in-law worked at Disneyland and got us free passes whenever we wanted, which was a lot. I went on every scary ride they had at the time, including that tower thingamabob, but that was when I was younger and knew everything. No more.

    Characters shouldn’t be totally fine one second then immediately immobilized by terror. Let emotions build over time, even second by second.

    In my newest novel release, in one scene in the middle of the story, the MC thinks her 3 year old daughter has been taken from the local park. I strung that fearful scene out over about 22 pages, as she navigated every Mom-fear ever. I drew from an experience I had long ago when we couldn’t find our toddler son for a few minutes at a park.

    It kind of worried me to make it so many pages, but my editor was with me on it.


    • Deb, I bet it worked well. Fear building to a crescendo makes for an exciting reader experience. In my latest, Merciless Mayhem, it opens with an abduction and the fear builds and builds for several chapters. Then I let the reader catch their breath for a minute before plunging them back into the depths of despair. 😉

  10. Thanks. A lot of helpful info to consider when writing our stories. As for me, sorry, not an adrenaline junkie. Dealing with every day life is challenge enough. LOL!

  11. Speaking of adrenaline junkies, my studies lead me believe that bipolar disorder is a form of adrenaline addiction. It’s striking how close the mania and depression phases of BD match the euphoria and withdrawal stages of drug addiction.

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