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Common Signs of Illness in Dogs: What to Look For

October 18 2025

As a pet parent, you know your dog’s habits, energy, and quirks better than anyone. But sometimes, even the most attentive owner can miss the early signs of illness. Dogs can’t tell us with words when they’re not feeling well, but they do communicate through subtle physical and behavioral changes. At Animals First Veterinary Hospital, your Haddon Township, NJ, vet clinic, we help families learn what to watch for so health concerns can be caught before they become serious.

This guide outlines common warning signs of illness in dogs, from subtle shifts in behavior to clear physical symptoms, and what steps you should take if you notice them.

Changes in Appetite and Thirst

One of the most obvious signs something is wrong is a change in eating or drinking habits.

  • Loss of appetite: May signal infections, dental problems, digestive upset, or systemic illness.
  • Increased appetite: Can be linked to metabolic conditions like diabetes or thyroid issues.
  • Excessive thirst or urination: Often connected to kidney disease, diabetes, or hormonal imbalances.

A single skipped meal may not be cause for panic, but consistent changes warrant a veterinary exam.

Click here for our earlier pet emergency blog post. 

Lethargy or Reduced Activity

If your usually playful pup is suddenly disinterested in walks or toys, it’s often a red flag. Lethargy can stem from infections, pain, or more serious systemic illnesses. Even mild fatigue, if it persists, should be checked out—dogs rarely act tired without a reason.

Digestive Issues

Occasional stomach upset happens, but ongoing digestive problems are a different story.

  • Vomiting: Frequent or severe vomiting should be addressed quickly.
  • Diarrhea: Chronic loose stools can lead to dehydration and signal underlying disease.
  • Constipation: May indicate dehydration, diet issues, or obstructions.

Persistent digestive changes should always be evaluated by your veterinarian.

Respiratory Symptoms

Coughing, sneezing, or labored breathing may indicate anything from kennel cough to heart disease. Watch for:

  • Persistent cough or wheezing
  • Labored or noisy breathing
  • Nasal discharge, especially if thick or discolored

Any breathing difficulties are urgent and require prompt veterinary attention.

Skin and Coat Changes

Your dog’s skin and coat reflect their health. Warning signs include:

  • Excessive scratching, licking, or biting
  • Bald patches, sores, or scabs
  • A dull, flaky, or greasy coat

These may point to allergies, parasites, or systemic issues affecting skin health.

Behavior and Mood Shifts

Dogs often show illness through behavior. Be alert to:

  • Increased irritability or aggression
  • Restlessness or difficulty sleeping
  • Withdrawal from family members
  • Sudden anxiety or clinginess

Any unexplained shift in mood can be a clue your dog isn’t feeling well.

Weight Loss or Gain

Unexplained weight changes should never be ignored.

  • Weight loss: May be caused by parasites, metabolic disorders, or chronic illness.
  • Weight gain: Could result from overfeeding but also from thyroid disease or other metabolic problems.

Gradual changes can creep up unnoticed, so regular weigh-ins are helpful.

When to Seek Veterinary Care

If you notice one or more of these signs, it’s best to schedule an exam. Dogs often hide illness until it’s advanced, so early intervention is critical. At Animals First Veterinary Hospital, we can run diagnostics, perform a thorough exam, and provide a treatment plan to restore your dog’s health.

The AKC has an article on signs of illness in dogs, which you can read here.  Purina also has a blog about signs of illness in dogs, which is here

FAQs About Dog Illness Signs

1. What is the most common early sign of illness in dogs?
Changes in appetite or energy are often the first red flags.

2. Should I worry if my dog vomits once?
Not necessarily, but if vomiting is frequent or severe, see a vet.

3. Can dogs hide illness well?
Yes, many dogs mask symptoms until the condition is advanced.

4. How do I know if my dog’s cough is serious?
If it’s persistent, harsh, or paired with breathing trouble, seek veterinary care immediately.

5. Are annual exams really necessary if my dog seems healthy?
Yes, routine exams help catch subtle health problems before they become severe.

Make An Appointment At Our Haddon Township, NJ, Vet Clinic

Recognizing the early signs of illness in your dog could make the difference between a quick recovery and a serious condition. By staying attentive to changes in appetite, energy, skin, and behavior, you can help your dog live a longer, healthier life. At Animals First Veterinary Hospital, your Haddon Township, NJ, pet clinic, we’re here to partner with you in keeping your pup at their best. If you’ve been searching for a “vet near me” to help ensure your dog’s well-being, our compassionate team is here for you.

Click here to go to our Service page and find out more about our animal clinic and the pets we treat. You can also learn about our critical care and emergency pet services here, or our membership plans here.

Disclaimer: This blog is for informational purposes only and should not replace professional veterinary advice. Always consult with your veterinarian for diagnosis and treatment tailored to your pet.

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Animals First + Veterinary Hospital is your trusted veterinary partner in Haddon Township, NJ. We are committed to providing the highest standard of care for dogs, cats, birds, exotic pets, and small mammals. Our services include laser therapy, acupuncture, wellness care, behavioral counseling, and emergency care. 

We treat every pet with kindness and a gentle touch. 

Contact us today at (856) 946-7788 to schedule an appointment or visit our Service Page to learn more about the care we offer and the pets we treat.

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