Ears back. Body trembling. Hiding in the bathtub or crawling under the bed. The telltale signs of a scared pup are familiar to dog owners, and they’re especially common in summer, when fireworks and thunderstorms can heighten dogs’ anxiety levels. But while the sight of a sparkler sends some dogs tail-tucked and running, others remain unfazed by booms and bangs.

To sort out this canine confusion, dog researchers around the world are investigating what makes dogs react to sounds with fear. Better understanding canine fear behaviors could improve dogs’ quality of life and even help to explain human fear responses.

The sound of fear

Dogs are known for their olfactory prowess, but sound also dictates their experience of the world. Dogs hear more than twice as many frequencies as humans, and they can also hear sounds roughly four times further away. Reacting to every sound would demand too much energy, and so dog brains must determine which sounds are significant and which can be tuned out. This “auditory flexibility” is especially important for working dogs; for example, lives depend on the ability of military dogs and detection dogs to remain calm despite the loud sounds and explosions they may encounter.

On the other hand, evolution has trained most animals, including dogs, that avoiding a perceived threat is worth it for overall survival, even if, as in the case of fireworks, the threat doesn’t end up being real.

“From a biological perspective, it pays to err on the side of running away even when it’s not necessary. So why does my dog have a tendency to be anxious? Well that’s a normal trait,” says Daniel Mills, a professor of veterinary behavioral medicine at The University of Lincoln in England.

For some dogs, early life conditioning can make the difference in their sensitivity to sound. Like human infants, puppies undergo critical stages of development when their brains form associations that can influence behavior for the rest of their lives. If, for example, a construction worker was hammering the wall in a neighboring apartment while a puppy was left home alone, that puppy might associate banging with abandonment—without her owner even knowing it had happened. That association could trigger a fear response in the dog every time she heard a bang.

“Puppies have this period where their brain learns what is normal in the world, what is okay and what should I not be afraid of. And then after 12 weeks of age [about when most dogs are adopted], they start to develop their fear response. So, if they encounter something new after three months of age and it frightens them, they can learn to be afraid of that going forward,” says Naomi Harvey, Research Manager in Canine Behavior at Dogs Trust .

Stress genetics

Dogs that have little to no negative associations with loud sounds can still be found cowering during a storm, while others who had a scary early experience can learn, often through counterconditioning and desensitization, to overcome the fright. One explanation for this can be found in temperament. Unlike personality and mood, which are more fluid emotional states, temperament is a deeper, more hardwired system affected by genetics and early development. Temperament is shaped by epigenetics, or the way an animal’s genes are influenced by external factors, and this can play a significant role in the dogs’ inherent predisposition to stress, anxiety and fear.

For example, studies in humans and animals show that mothers who experience high levels of stress during pregnancy can pass on a propensity for anxiety to their young via the stress hormone cortisol. When signaled by a stress-inducing event, the brain’s hypothalamic-pituitary-adrenal axis (HPA) becomes active and produces cortisol, which then travels throughout the body keeping an individual on “high alert.” High cortisol levels in the mother’s bloodstream have subsequent negative effects on the developing baby, or in this case, puppy.

Scientists have measured cortisol levels in dog hair to study the relationship between the dogs’ internal stress response and their behaviors in response to loud noises, such as hiding or shaking. One study found that cortisol levels from dogs who had listened to the recording of a thunderstorm were higher than those who listened to regular dog sounds and barks. The dogs with higher cortisol levels in their hair also showed high rates of hiding, running away and seeking attention from humans when exposed to the storm sounds.

In a more recent experiment with a group of border collies, dogs who showed greater signs of fear and anxiety toward loud noises actually had lower concentrations of cortisol in their hair. This sounds contradictory. To explain the finding, the team hypothesized that that “these dogs may have become dysregulated following chronic exposure, leading to a state of HPA hypoactivity, or ‘vital exhaustion’.” In other words, the dogs felt such constant anxiety that their internal mechanisms no longer responded, not dissimilar to chronically stressed humans who feel they can no longer cope.

Still, a dog does not have to be temperamentally fearful to suffer from a noise fear. In several studies of fear responses to noises, researchers find that factors such as breed, age, sex, reproductive status, length of time with owner, and early exposure to certain loud noises all impacted how dogs reacted to sounds like fireworks. Dogs living with an owner who bred them had reduced risk of fear compared to those with a second owner, for instance, and certain breeds compared to mixed-breed dogs were more prone to display fearful behavior.

Fear risk increases with age in dogs, which can be connected to pain, but also to how they perceive sound. Older dogs first lose the ability to detect higher frequency sounds, which give important location cues. The inability to locate sounds can increase the severity of stress for a dog. “Hearing the noise and not knowing where it’s coming from is probably much scarier for a dog, and this is why fireworks are much scarier for a dog,” Mills says. “You can watch a fireworks display and know that it's not going to hit your balcony. But if you’re a dog, all you know is there’s a bang there, a bang there, and I don’t know the next bang isn’t going to happen here.”

The best defense

According to a new study in the Journal of Veterinary Behavior , one tactic is the clear frontrunner for dealing with firework fear: preventing fear from developing in the first place.

Stefanie Riemer, who studies dogs and their emotions with the University of Bern’s Companion Animal Behavior Group in Switzerland, analyzed the management and treatment methods used by 1,225 dog owners who responded to a survey and correlated those methods with an increasing or decreasing fear score. Riemer asked the owners of dogs with a known fear of fireworks to select from a number of interventions and treatments and report on how the pups fared during New Year’s fireworks displays. The methods included noise CDs to drown out the sound, pheromone diffusers, herbal products, homeopathic products, essential oils, prescription medications, relaxation training, counterconditioning (trying to train the dogs not to be afraid) and the use of wearable pressure vests that can have a calming effect.

Riemer found that at-home counterconditioning was one of the most effective ways to alleviate the dog’s stress. When the fireworks started, owners played with the dog, gave treats and expressed positive emotions. Dogs who received this counterconditioning were 70 percent less scared during fireworks, on average, than dogs who did not. “Counterconditioning—I think that would be probably the most important advice to any owner especially with a new puppy or a new dog,” she says. “Even if they do not yet show any fear of noises, keep it that way.”

“There’s a myth that you’re by reacting positively you’re reinforcing fear, which you can’t do because fear is an emotion not a behavior,” adds Harvey, who was not involved in the study.

However, because not all dogs can receive this kind of training or will be receptive to it, Mills and his colleagues have developed the Lincoln Sound Sensitivity Scale (LSSS) for owners to assess where on the fear spectrum their dog’s anxiety falls. “When an animal has a fear of fireworks, what we mean is [that animal] shows a large reaction to firework noises. What we’re interested in is how big is that response,” says Mills.

Once owners are able to accurately determine their individual dog’s fear level, they can then work with a veterinarian to choose the most effective method for treatment, which may include medication. The LSSS will soon be available as a phone app, and the developers hope it will be ready in time for this year’s Fourth of July and summer celebrations.

As a society, people are just beginning to accept that dogs, like humans, have emotions. And part of caring for canines means supporting their emotional health. The more we learn about the complexities of dogs’ emotional states, the better equipped we will be to keep their tails happily wagging.