Dogs have an incredible sense of smell that allows them to detect subtle changes in odors that humans can’t perceive. Their powerful noses paired with their pack mentality means that dogs often seem to “just know” when another canine is feeling under the weather before symptoms become outwardly apparent.

But is it true that dogs can actually tell when other dogs are sick?

If you’re short on time, here’s a quick answer to your question: While definitive scientific evidence is lacking, most experts agree that dogs likely have the ability to detect when other dogs are sick or injured through their acute sense of smell.

Their pack mentality and social nature also contribute to this uncanny perception.

Dogs Can Smell Subtle Biological Changes

Their Nose Knows

Dogs have an incredibly sensitive sense of smell thanks to their 220 million olfactory receptors (compared to humans’ 5 million). This allows them to detect subtle changes in scent that may indicate illness or disease. When a person or animal is unwell, their body chemistry changes ever so slightly.

While these changes may be imperceptible to humans, dogs can pick up on them easily.

For example, dogs can smell increased ketones on someone’s breath when they have diabetes, or detect changes in skin cells and sweat when cancer is present. They can also sniff out inflammation associated with joint issues like arthritis.

Their nose literally knows when a smell doesn’t seem quite right – even if the difference is not obvious to medical tests at first.

Smelling Cancer and Other Diseases

There are many stories of dogs alerting their owners to undiagnosed cancer or other medical conditions. Dogs have been trained to detect specific types of cancer through smell, including prostate, bladder, colorectal, breast, and ovarian cancers.

In studies, trained dogs have been able to identify urine and stool samples from patients with these cancers with up to 97% accuracy. Their early detection could allow for earlier intervention and improved outcomes for patients.

Beyond cancer, dogs can also smell other diseases in advance, like migraines, low blood sugar in diabetics, and seizures. Some theories suggest the dogs are reacting to subtle changes in skin odors, breath, sweat, or hormonal levels.

Whatever the cause, it’s clear dogs can pick up on the smallest odor changes linked to disease.

While more research is still needed, the dog’s spectacular sense of smell has amazing potential to detect illness early on. Your dog nudging you may actually be their way of saying – please get checked out, I smell something different about you!

So don’t dismiss their concerns – dogs really may know more about our health than we realize.

Dogs Have a Pack Mentality

Looking Out for the Pack

Dogs are pack animals by nature and have retained many of their wolf-like instincts and behaviors. One of the most important pack behaviors for survival is looking out for each other and responding to signs of weakness or sickness. Here’s why dogs seem to know when other dogs are not feeling well:

  • Dogs use their powerful sense of smell to detect changes in the health of other pack members. Their noses can pick up subtle differences in body odors that may indicate illness or injury.
  • Dogs are very attuned to body language and behavior changes in other dogs that may signal weakness or sickness – things like lethargy, weakness, changes in gait or posture, changes in interactions with other dogs, or loss of appetite.
  • Dogs have evolved to hide outward signs of pain or sickness to avoid appearing weak to predators. But other pack members seem able to sense when something is “off” through other cues.
  • When a dog appears ill or hurt, other pack members often provide comfort through gentle licking or nuzzling, or try to get the sick dog to move to the den site for rest and safety.

In essence, dogs are wired to detect vulnerabilities in pack mates that might threaten the strength and cohesion of the overall pack. Recognizing sickness allows the pack to adjust behaviors to protect vulnerable members.

Responding to Weakness or Injury

When dogs sense that another dog is unwell, their pack instincts kick in and they typically respond in ways meant to comfort or protect the affected dog. Here are some common responses:

  • Providing comfort through physical contact and companionship. Dogs may lick, nuzzle, lay near, or lean against the sick dog.
  • Alerting the rest of the pack. Dogs may bark to draw attention to the unwell member.
  • Limiting interactions with the sick dog to prevent contagion or further injury. Dogs tend to avoid rough play or antagonistic interactions with an injured or sick companion.
  • Bringing the sick dog food or encouraging eating/drinking. This instinct comes from pack reliance on every able member to hunt/forage.
  • Guarding or “babysitting” an injured or weak dog, staying close to provide protection.
  • Gently nudging or encouraging movement away from danger and toward shelter or the pack for safety and rest.

Dogs Pay Close Attention to Each Other

Observing Behavioral Changes

Studies have shown that dogs possess an innate ability to detect sickness in other dogs. As highly social pack animals, dogs have evolved to closely observe the behavior of those around them for any abnormalities that could signal illness or weakness (1).

Things like changes in playfulness, activity levels, appetite, and demeanor can quickly catch a dog’s attention.

For example, dogs that are feeling under the weather tend to sleep more, play less, and withdraw from social interaction. Healthy pack members notice when a play bow or game of chase is declined. A sudden disinterest in play is abnormal dog behavior, especially in young dogs.

Additionally, a normally ravenous dog that leaves his dinner uneaten will perk up curiosity from canine housemates. Loss of appetite in dogs almost always indicates an underlying health issue.

Noticing Lethargy or Loss of Appetite

Vomiting, coughing, limping, and other more obvious symptoms also put dogs on alert that something may be wrong with a companion. However, even subtle shifts like moving stiffly post-exercise or lack of initiative to go on a walk prompt doggy concern for a four-legged friend.

Dogs experiencing illness or injury sometimes emit different scents due to physiological changes. While humans may not detect anything amiss, dogs with an exceptional sense of smell can sniff out these differences.

Research suggests dogs may be capable of literally smelling fear or sadness on both canine and human counterparts.

Because survival of the pack requires all members to pull their own weight, dogs are motivated to notice when one of their own isn’t quite up to par. In one Hungarian study, dogs reacted to other dogs that were not given food by refusing to cooperate with researchers on a task (2).

This indicates awareness of unfair treatment. As social animals, dogs have an interest in each other’s welfare. Close bonds between co-habitating dogs mean roommate pups may even refuse treats or meals when the other dog is sick and unable to eat as well.

Limitations of Our Understanding

While research has shed light on dogs’ ability to detect illness in other dogs, there are still many unanswered questions and limitations in our current understanding:

Lack of Scientific Studies

There have been very few scientific studies investigating dogs’ detection of illness in other dogs. Much of the evidence so far comes from anecdotal reports from dog owners and trainers. More controlled, empirical research is needed to truly understand this phenomenon.

Mechanisms Not Fully Understood

It is unclear exactly how dogs are able to detect sickness in other dogs. Proposed explanations include detection of odor cues, behavioral changes, or other physiological signs that dogs can sense. But the specific mechanisms have not yet been identified through research.

Limitations of Dog’s Abilities

While dogs seem able to detect some illnesses, they likely cannot detect all diseases or pre-clinical stages. Their sensitivity and specificity in illness detection is unknown. It is also unknown whether some dogs are better at detection than others.

Role of Dog-Dog Familiarity

It is not clear if dogs are better able to detect illness in dogs they are familiar with compared to unknown dogs. Most evidence of illness detection comes from dogs living together, but their capabilities with unfamiliar dogs requires further study.

Limitations of Owner Reports

Much of the evidence for dogs detecting illness comes from owner anecdotes. Owners may misinterpret their dogs’ behavior or may be subject to confirmation bias. Controlled studies are needed to truly evaluate dogs’ capabilities.

Lack of Standard Training Protocols

While some dogs have been trained to detect diseases like cancer, there are no standard protocols for training dogs to detect illness in other dogs specifically. The best methods for developing and evaluating this ability are unknown.


While science has not definitively proven that dogs can detect illness in other canines, their evolutionary traits and pack mentality provide compelling evidence that they likely possess this ability.

Their incredibly sensitive noses can pick up on subtle scent changes caused by biological shifts, allowing dogs to sense health problems and vulnerabilities. Combined with their natural vigilance towards the wellbeing of their fellow pack members, it makes sense that dogs seem to intuitively recognize when another dog is feeling under the weather.

So while your pup may not be able to diagnose exactly what is wrong with their daycare buddy, chances are they do know on some level that their furry friend isn’t feeling quite like themselves.

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