Your dog isn’t acting like his usual playful, cheery self. How do you know if he’s having an off day, or a health problem?

Dogs, like little kids, can’t really tell you when they’re sick, so it pays to learn the signs. If your furry best friend has any of these 13 symptoms, it’s worth a trip to the vet.

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1. Poop problems. Diarrhea for more than three days or loose stools along with other symptoms such as vomiting, not eating or acting lethargic are signs that require a vet visit.

“Diarrhea can cause dehydration and can be life threatening to small dogs,” says Krista Vernaleken, DVM, medical director at Bulger Veterinary Hospital in North Andover, Massachusetts.

Black tarry stools should also be checked by a vet, adds Vernaleken. They’re a sign of digested blood in the stool and could mean a stomach ulcer.

2. Vomiting. One vomit is not necessarily a concern, says Vernaleken, especially if your dog looks fine. But throwing up more than once in a day, vomiting fluids or yellowish material or throwing up and being lethargic are all emergencies. These could be signs of a gastrointestinal obstruction, hormonal imbalances, electrolyte abnormalities, poisoning, liver or kidney dysfunction, pancreatitis and cancer.

Also, your dog trying and being unable to vomit could be a serious emergency called gastric dilatation-volvulus or bloat, explains Greg Wolfus, DVM, director of Tufts at Tech Veterinary Clinic at Tufts University’s Cummings School of Veterinary Medicine.

3. Restless behavior. If your dog is pacing, anxious, whining, shaking or looking distressed, he’s uncomfortable and you should bring him to the vet right away. His belly could be hurting, he may have a urinary tract infection, have neck pain or something else, says Vernaleken. “These symptoms could be a sign of some very serious illnesses.”

4. Excessive thirst and peeing. These generally go together, and many dog owners miss them, says Vernaleken. Take your dog to the vet right away, as he may have an illness that requires immediate treatment such as kidney failure, diabetes, liver problems or hormonal issues.

Sick dog (Photo: Igor Normann/Shutterstock)

5. Lethargy or unresponsiveness. If it’s hot outside, it might make sense for your dog to be lethargic. But if he’s not in the mood for anything and you can’t figure out why, take him to the vet, advises Vernaleken. “The dog may be anemic or have a fever,” says Wolfus, to name a few potential problems.

If your dog collapses or is unresponsive, that’s a serious emergency. Rush him to the vet, says Vernaleken.

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6. Sudden changes in eating habits. If your dog’s recovering from an illness or it’s very hot outside, it’s OK if she doesn’t eat that day, says Vernaleken. But if she’s always hungry and suddenly refuses food, take her to the vet. It could be dental disease, a kidney, liver or pancreas problem, a stomach bug, a hormonal imbalance or even cancer. “It could be a sign the dog’s in pain,” adds Wolfus.

If your dog is suddenly ravenous, it could be diabetes, intestinal problems, parasites or cancer, says Wolfus.

7. Weight loss. You think your dog is eating fine but he’s losing weight. Take him to the vet right away. Cancer is a strong possibility, says Vernaleken, or it could be a kidney or liver problem or a hormonal imbalance, among other things.

8. Breathing problems. Struggling for air, wheezing or making other breathing sounds are emergencies, says Vernaleken. They could signs of bronchitis, heart disease, trachea collapse or larynx paralysis.

Persistent or progressive coughing or acute coughing should also be checked right away, says Wolfus. They could mean kennel cough, influenza, pneumonia, heart disease, heartworm disease or even cancer.

9. A distended belly. A distended abdomen could be a sign of internal bleeding, bloat or a hormonal disease — all emergencies, according to Vernaleken.

10. Limping. If your pooch is having difficulty walking, he’s in pain and should see a vet, alerts Vernaleken. It could be something mild or a ligament tear, a fracture, a tick-born disease such as Lyme or even arthritis, says Wolfus. 

labrador with empty food bowllabrador with empty food bowl (Photo: Jaromir Chalabala/Shutterstock)

11. Eye problems. If your dog has red eyes, is blinking a lot or pawing at the face, have him checked right away. It could be a corneal scratch or ulcer, a detached retina, glaucoma or even a breed-specific illness such as dry-eye syndrome, says Wolfus. “Any eye issue is an emergency."

12. Ear problems. If your dog is shaking her head, scratching her ears or if you notice redness, swelling, a bad smell or any discharge in the ear canal, that may be a sign of yeast, ear mites, bacteria or even allergies, says Vernaleken. Time for a vet visit.

13. Skin issues. If you pooch is scratching, licking or biting himself, has a hot spot or hair loss in an area, take him to the vet. It could be allergic dermatitis, fleas or even allergy to fleas, says Vernaleken.

The best way to protect your dog’s health, says Wolfus, is by knowing him well and monitoring and recording his main functions — how many times he poops and pees a day and how they look — as well as eating behavior.

“It’s much easier to identify a problem if you have reliable information,” says Wolfus, especially in a household where several people are feeding and caring for the dog.

If you feel something’s wrong and it’s after hours, call an emergency vet hospital to discuss if it’s worth bringing your dog in. And always trust your gut, says Wolfus. “If someone tells me something’s wrong with their dog,” says Wolfus, “nine times out of 10 they are right.”

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Daniela Caride is a freelance writer who has four cats and two dogs. She blogs about being a pet parent at Taildom.com and founded a nonprofit called Phinney's Friends.