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Trigger Stacking: When Stress Builds Up & Your Dog Reacts

Has your dog ever reacted seemingly out of nowhere?

Maybe you were out on a walk and your dog was doing well encountering other dogs, or a car backfiring, or kids screaming, and then -- when a jogger ran by -- he started lunging and snarling. Or maybe your dog got an A+ behavior report from the vet and then that evening a package arrived and your usually mild-mannered dog went nuts at the front window. Or perhaps you had a holiday cookout. Lots of guests, family, friends and neighbors arrived throughout the day. Your dog was having a blast and happily playing fetch with the kids. Later, when she was resting, a child came up to pet her and she snapped at him, surprising and upsetting everyone.

The phenomenon of trigger stacking might be the reason.

What is Trigger Stacking?

Trigger stacking is when your dog is exposed to more than one stressful event in a short period of time, usually one to 24 hours but sometimes up to days.

The stressful events don’t need to be traumatic, they might just be annoying.

Consider your last “bad day.” I remember one years ago: I didn’t sleep very well the night before, I’d had a cup of coffee too late in the day. That morning, as I was getting out of the shower, I slipped on the floor and stubbed my toe. No blood, and a couple of four-letter words whispered under my breath took care of the pain.

I picked up my mail, paid a couple of bills. As I was driving to the grocery store, some jerk with road rage slammed on his horn and then cut me off. The store was out of my favorite brand of oat milk. When I got home, someone was in my usual spot so I had to park a couple blocks away and take two trips to carry my groceries. All of these were pretty mundane and minor stressors that most people can handle pretty well, myself included.

Not My Finest Hour

But then I sat down to look at my social media. A troll had been in my comment section, leaving nasty words about rewards-based training, making specious claims about my experience, throwing in a few ad hominem attacks, and generally doing what internet trolls do. My heart rate skyrocketed, I felt my face get hot and… I reacted. I defensively responded to each comment in turn, spending more time than I’d like to admit, thumbs-a-blur, on some random guy who I’d never met, heard of, or typically would care about.

My normal chill-and-thoughtful self would’ve simply deleted the comments, blocked the offender and moved on with my life. I knew how to deal with internet trolls. ("He's usually great with visitors!") But because of all the minor annoyances earlier that day, my brain and body were primed for fight-or-flight. I was already swimming in stress hormones and it didn’t take much (a single, troll-shaped straw) to break into emotions of blind, defensive rage.

I eventually came to my senses, blocked the guy and haven’t had a problem since, but man it took hours for me to calm down. I actually didn’t fully recover for a few days. What a waste of my energy!

This same phenomenon can happen to non-human animals, including our beloved dogs.

Clouded Judgement

When animals (including humans) are overly stressed, our cognitive “thinking brains” pretty much go off-line (McKlveen 2016). Whatever acquired skills we’ve learned fly right out the window and we return to our basest, lizard-y selves. It’s not pretty but it’s totally normal, for humans and for dogs.

Typically this trigger-stacking phenomenon is something that starts to rear its ugly head when you’ve already made some serious progress with your dog. You’ve learned how to use management to lower your dog’s stress levels. You’ve used positive reinforcement to teach some new skills. Your dog’s behavior is starting to improve, slowly at first, and then pretty dramatically. You become a believer in using food and fun games to change emotions and behavior. And you might even get a little over-confident.

She Was Doing So Well and Then: BOOM!

So, when you’re out with your dog and she’s doing well, passing triggers like they’re nothing and then, seemingly out of nowhere she reacts, you might at first scratch your head. “She’s never been aggressive to kids,” or “She hasn’t barked at the neighbor’s dog in months!” or you start to think, “This treat-training thing isn’t working.”

What’s really happening is you didn’t think about the tiny amounts of stress that built up to that final reaction.

One of the many things that stinks about stress is that it is cumulative (Conrad 2008). Once fired, stress hormones swim around in the brain and body for a while, and it takes time to come back to baseline. For healthy dogs, sometimes as short as an hour (Beerda 1998). For dogs with health issues, who’ve experienced traumatic events or have chronic stress, it can be days.

Look at the graphic below of Yuki the Shiba Inu and how she is able to handle minor stressors like car rides, pets from a stranger, and both familiar and unfamiliar dogs.

Yuki has lots of dog friends she sees at playdates. One of them is Luna, her BFF.

One day, Yuki snarled at Luna as soon as she approached, which was very surprising to everyone. With a little detective work, I discovered that Yuki had ridden in a car, received pets from an unfamiliar person and had encountered an unfamiliar dog who growled at her, all within an hour before seeing Luna.

Yuki didn’t overtly react to any of those things, but her patience was waning. Luna inadvertently tipped Yuki over into “I’m upset!” territory.

So what do we do for dogs who aren’t able to handle all these triggers together? There are lots of ways to raise a dog’s threshold for a reaction:

  • Rest breaks in a safe and quiet environment

  • Give your dog freedom to make some of their own choices

  • Predictable routines

  • Opportunity to sniff, chew, dig, play, forage

  • Winnable food-puzzles

  • Create happy emotions to even very minor stressors through counter-conditioning

  • Avoid punishment (imagine if someone yelled at you when you were already stressed out!)

  • Count triggers & stop exposure if the count gets too high

  • Carefully watch your dog's body language for early signs of stress

  • Avoid under- or over-exercising

  • Rule out medical causes or contributors with your veterinarian

  • Discuss nutrition with your veterinarian

  • Discuss pharmacological options with your veterinarian (chronic stress and anxiety are clinical issues, with serious short and long-term health effects)

Teamwork with your vet, a qualified behavior consultant or trainer, and an incremental exposure plan individualized for your dog (as well as data tracking!) will yield the best outcomes.


Need help with your fearful or reactive dog? Schedule an initial consultation for comprehensive, individual support.

Or sign-up for my "Life Skills" class for shy & fearful dogs or my leash reactive class with Bravo!Pup.

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