Is It Reactivity… or Is It Pain? Subtle Signs Your Dog Might Be Hurting

It can be deeply unsettling when your dog growls, snaps, or suddenly seems “off” around you or your loved ones. You might find yourself wondering, Where did this come from? or even worse, Can I keep my dog if this continues? The thoughts may start flooding in: wondering if you’ll need to rehome your dog to protect your children, or if you just need to shrink your presence and walk on eggshells at home to avoid provoking them again.

But before jumping to conclusions about their sudden new behavior being a training issue, it’s important to look deeper into some of the most common hidden culprits of sudden behavior change: pain, inflammation, and discomfort. 

We tend to think of pain in dogs as something dramatic: like limping, crying out, or yelping. But the reality is, most discomfort in dogs is much more subtle. It can show up in quiet, everyday moments that are easy to miss. If we don’t catch those signals, we may unintentionally respond in ways that escalate the issue or even harm the trust we’ve built...leading to a frustrating and emotionally draining cycle for both you and your dog.

Why Pain Can Look Like Reactivity

If you’ve ever had a migraine or terrible stomach cramps, it’s probably no surprise that your stress tolerance was significantly lower in those moments and so was your patience with others. Maybe your partner tried to be playful, and you snapped at them to back off, or your kids were listening to their iPads too loudly, and you just couldn’t take one more second of it. In those moments, your system is already overwhelmed, and even small, everyday things can feel like too much.

You might also catch yourself “pushing through” for a really fun activity and before you know it, you’re horseback riding in Costa Rica even though an hour ago you could hardly stand and were on puke watch (hi, this is me, this actually happened). This doesn’t mean the pain or illness you were experiencing actually went away, but rather that the dopamine your body produces in preparation for the fun activity helps act as a pain reducer, along with the adrenaline while you’re doing it!

Dogs experience something similar. When they’re in pain or discomfort, their ability to handle everyday stressors decreases. They may react more intensely to things that once felt neutral, avoid physical touch, or even seek out high-adrenaline activities: like obsessive ball chasing, zoomies, rough play, or chasing squirrels, as a way to subconsciously self-medicate. That’s because dopamine and adrenaline act as natural pain relievers for dogs too!

It’s also important to understand that pain doesn’t look the same in every individual or every dog. There are different types and severities of pain, inflammation, and discomfort and each individual has different thresholds and ways of expressing it. What’s tolerable for one dog might be unbearable for another.

And there’s a sneaky culprit that amplifies pain responses: stress and anxiety. Just like in humans, when a dog’s baseline level of stress is elevated, their perception of pain becomes more intense and harder to regulate. For some, the pain is sharp and acute. For others, it becomes a constant, dull hum in the background of daily life, quietly shaping their behavior.

Before jumping to conclusions or labeling a dog as "reactive," "defiant," or "aggressive," it’s worth pausing to ask: could pain be part of the picture?

Subtle Signs Your Dog May Be In Pain

1. Hesitation and Avoidance With Posture Changes

This is one of the most common pain-related behaviors I see. A dog may hesitate before going down stairs, jumping up, or performing previously known cues like “sit.” They may even avoid certain rooms with slippery surfaces altogether. One simple “data test” I walk clients through is observing whether their dog responds to the cue “sit” more quickly on carpet than on slippery flooring. Slippery surfaces can cause dogs’ legs to slip out, creating extra strain on their joints and causing acute pain when it happens. Adding more carpet or rugs in your home—especially in areas where your dog tends to run or jump on and off furniture—can help make them more comfortable. You can also consider getting pet stairs or ramps to assist your dog with furniture access and reduce joint strain.

2. Muscle Atrophy & Hair Growth Changes

If your dog suddenly feels more “boney” or less sturdy, especially in the hindquarters or shoulders, that could be muscle atrophy from underuse. Muscle atrophy in dogs may not always be painful in of itself, but can be associated with pain from underlying conditions or exacerbate existing pain. If dogs are injured or have arthritis, they may favor one limb more than another or reduce their overall activity and movement leading to more muscle atrophy. This weakness makes it more difficult for them to stand up, walk, and have endurance for normal activities. Another thing to check out for is sudden changes in hair growth on your dog such as unusual whorls, cowlicks, tufts, thinning, or changes in hair texture. These symptoms are usually indicative of underlying muscle tension, causing the skin and fur to tense and change. If you notice these signs, you can consult with your veterinarian to discuss potential pain remedies or look into an anti-inflammatory diet. 

3. Stiff or Abnormal Gait

Pay attention to how your dog moves. Are they favoring one side? Do they look stiff anywhere? Do they have a shortened stride or bunny-hop with the back legs? Gait changes are a major red flag.

Pro tip: Watch videos of a normal dog gait here to familiarize yourself and compare by recording your own dog. Share your video with your vet or a rehab specialist for insight.

And if you want to contribute to research and the development of AI being able to diagnose abnormal gait changes in dogs early, you can submit a video of your own dog to the Canine Arthritis Management team here.

4. Sensitivity During Handling

Dogs who flinch, twitch, or whip their head toward you when touched may be reacting to discomfort, not just disliking the touch. Keep an eye out for:

• Lip licking

• Mouthing during handling

• Growling when buckling a harness or touching the ribs, hips, or belly

• Sudden snapping during grooming or petting

These behaviors are often chalked up to “bad manners” or “being dramatic” - when they’re actually communication of physical discomfort and a request for space.

5. Heat Cycles & Pain Sensitivity

If you have an intact female, be mindful that heat cycles can lower stress tolerance and make discomfort feel more intense. This can make even a normally tolerant dog more likely to react or escalate. Talking to your vet or vet nutritionist early, may be able to help your dog feel more comfortable and in less pain during their heat cycles. 

6. Nutrient Deficiencies Can Fuel Inflammation

Nutrient imbalances or deficiencies often fly under the radar but can contribute to chronic inflammation. If your dog is itchy, red, inflamed, or has persistent digestive upset, it’s worth digging deeper. I’ve seen cases where addressing diet made a world of difference in both mood and behavior. One of my favorite resources for this is Dr. Wolfe at Tula Vet Nutrition. 

Looking at Your Dog's Behavior as Clues

Pain isn’t always obvious, but it’s often speaking through your dog’s behavior. I’ve worked with dogs who were labeled as aggressive, reactive, or “difficult,” only to discover that pain was the real issue all along.

Like the dog who growled and snapped when the harness came out—later diagnosed with stomach pain, skin irritation in that area, and a vitamin B-12 deficiency.
Or the pup who suddenly began growling at their owners whenever they touched the dog's back, later to be discovered that they had osteoarthritis.
Or the normally tolerant dog who escalated quickly during play, quietly coping with a torn ligament.

These aren’t just isolated stories - they’re reminders that behavior is often a clue to something deeper, not necessarily the root of the problem itself. When we pause to look beneath the surface, we not only support our dogs' well-being but also deepen the trust and connection we share with them, often reducing aggression and reactivity as a natural result.

Want to go deeper? I talk more about this topic and share real-life case studies in my recent podcast episode:

Is It Reactivity or Pain? Recognizing the Overlap