10 Early Signs of Illness in Dogs Every Owner Should Know

We love our dogs like family, right? But unlike our human relatives, dogs can’t just say, “Hey, I’m not feeling great today.” That’s why knowing the early signs of illness in dogs is so important. Catching symptoms early can be the difference between a simple vet visit and something far more serious. Dogs are masters at hiding discomfort, so it’s up to us to be observant and proactive. Here’s a guide to help you spot red flags before they become full-blown emergencies.

Changes in Appetite or Thirst

Sudden Loss of Appetite

If your furry friend suddenly turns their nose up at food they usually devour, it’s a red flag. Skipping a meal here or there might not be serious—but going 24+ hours without eating? That’s worth a vet visit.

Increased or Decreased Water Intake

Drinking like a fish or barely touching the water bowl can signal issues like diabetes, kidney disease, or infection. Track their water habits closely.

Lethargy or Fatigue

Sleeping More Than Usual

A tired pup after a big play session is normal. But if they’re snoozing all day, skipping walks, or seem uninterested in life, it might mean something’s wrong.

Reluctance to Play or Walk

When a dog who used to zoom around the house suddenly doesn't want to fetch or go outside, it’s time to ask why.

Vomiting or Diarrhea

Dogs eat weird things—let’s be honest. So, a one-time episode of vomiting or a soft stool isn’t always a big deal. But when it becomes frequent, persistent, or severe, it’s a whole different story.

Occasional vs. Frequent Episodes

An occasional upset stomach could just mean your dog got into something they shouldn’t have—maybe trash, table scraps, or a new treat. However, frequent vomiting or diarrhea can indicate underlying problems such as: https://www.vet.cornell.edu

• Gastrointestinal infections

• Parasites

• Pancreatitis

• Food allergies or sensitivities

• Organ dysfunction (like liver or kidney disease)

The biggest concern with ongoing vomiting and diarrhea is dehydration, which can become life-threatening quickly—especially in puppies or senior dogs.

When to Be Concerned

Here are signs you shouldn’t ignore:

• Vomiting or diarrhea that lasts longer than 24 hours

• Blood in the vomit or stool (bright red or dark, tar-like)

• Lethargy or weakness along with vomiting

• Fever, panting, or restlessness

• A bloated or hard abdomen

Weight Loss or Weight Gain

Weighing your dog regularly might not sound like a priority, but even a few pounds up or down can signal something’s off. And since most dogs wear fur coats year-round, subtle changes are easy to miss.

Unexplained Weight Loss

If your dog is eating normally—or even more than usual—but still losing weight, it could mean:

• Diabetes

• Cancer

• Thyroid disorders

• Digestive tract issues (like malabsorption)

You should also pay attention to muscle tone and overall body condition, not just numbers on a scale.

Unexpected Weight Gain

Gaining weight without changes in diet or activity may seem harmless, but it could be a sign of:

• Hypothyroidism

• Fluid retention (linked to heart or kidney disease)

• Lack of exercise due to pain or joint issues

Sudden or steady weight gain should prompt a check-in with your vet to rule out medical causes and discuss a healthy plan.https://www.avma.org

Coughing, Sneezing, or Breathing Issues

Much like humans, dogs can experience upper respiratory issues—but in dogs, these signs may be more serious than just a “cold.”

Persistent Coughing or Wheezing

If your dog sounds like they’re hacking up a hairball (especially small breeds), they may have something like kennel cough, which is highly contagious. Persistent coughing could also mean:

• Collapsed trachea

• Heartworm disease

• Bronchitis or pneumonia

Wheezing or gagging noises, especially when excited or exercising, shouldn’t be shrugged off.

Noisy or Labored Breathing

Breathing should be smooth and silent. If your dog is making rasping sounds, panting excessively, or seems like they’re struggling to breathe even at rest, that’s an emergency situation.

Watch for these warning signs:

• Blue-tinged gums or tongue

• Flared nostrils

• Open-mouth breathing (especially in cats and brachycephalic dogs like pugs)

Breathing issues can escalate quickly, so don’t delay in seeking care.

Changes in Urination or Defecation

Your dog’s bathroom habits say more about their health than you might think.

Accidents Indoors

A potty-trained pup suddenly peeing indoors is not just a “bad dog” moment—it could signal:

• Urinary tract infection (UTI)

• Bladder stones

• Diabetes

• Cushing’s disease

Straining or Blood in Urine/Stool

If your dog is:

• Squatting without producing urine

• Straining to poop

• Whining while peeing

• Passing blood or mucus

Skin and Coat Issues

A healthy dog’s coat is shiny, soft, and relatively odor-free. If your pup’s skin or coat starts to change, it might be telling you more than just “I need a bath.”

Dryness, Flakiness, or Bald Patches

Dry, itchy, or flaky skin could mean:

• Allergies (food, environmental, flea bites)

• Poor nutrition

• Parasites (like mites or fleas)

• Hypothyroidism

Excessive scratching, biting, or licking is your cue that something’s wrong beneath the surface.

Lumps, Bumps, or Sores

Not all lumps are dangerous—but you should always get them checked out. Some could be:

• Fatty tumors (lipomas)

• Infected cysts

• Cancerous growths

Any bump that’s growing, painful, discolored, or bleeding should be examined ASAP.

Behavioral Changes

Your dog’s behavior is one of the biggest windows into their health. If they’re suddenly acting like a different dog, don’t assume it’s “just a phase.”

Increased Aggression or Withdrawal

A once-friendly pup becoming snappy or hiding more often could mean they’re in pain or feeling unwell. Painful joints, internal discomfort, or even neurological issues could be at play.

Sudden Anxiety or Restlessness

Is your dog pacing, whining, or acting nervous? Restlessness can be tied to:

• Cognitive dysfunction (in senior dogs)

• Thyroid imbalances

• Internal pain or bloating

• Discomfort from infection or injury

Never ignore a behavioral shift—it’s your dog’s way of saying “something’s not right. https://www.akc.org

Bad Breath or Dental Problems

Foul-Smelling Breath

Doggy breath shouldn’t clear the room. If it does, dental disease might be progressing, which can also affect organs.

Drooling or Pawing at Mouth

Excessive drooling, bleeding gums, or signs of pain while eating should never be ignored.

Eye or Nose Discharge

Watery, Yellow, or Green Discharge

Clear discharge might be allergies, but colored or thick discharge usually means infection.

Cloudiness or Redness in Eyes

This could signal conjunctivitis, corneal ulcers, or glaucoma—all requiring prompt care.

Conclusion

Your dog can’t speak—but their body does. By staying observant and knowing what signs to look for, you’re not just being a good pet parent—you’re being a lifesaver. Don’t ignore the little changes. Trust your gut and, when in doubt, call your vet. After all, they’re more than pets—they’re family.

FAQs

What’s the most common early illness in dogs?
Digestive issues like vomiting or diarrhea are among the most common early signs that something's off.

How can I tell if my dog is in pain?
Signs like limping, whining, reluctance to move, or sudden behavioral changes can indicate discomfort or pain.

Are behavioral changes always a sign of illness?
Not always—sometimes it’s stress or aging—but they can definitely signal health problems, especially when paired with physical symptoms.

What should I do if I notice one or more of these signs?
Monitor your dog closely, jot down symptoms, and contact your vet. Early action makes all the difference.

How often should I take my dog to the vet?
At least once a year for a general check-up—more often if they’re seniors or have ongoing health issues.