How Can You Tell if Your Dog Is Sick? Signs to Know

Dogs cannot tell you they feel off. Worse, many are experts at hiding it — an instinct that made sense for their ancestors and makes life harder for the people who love them.

The good news is that you already know your dog better than anyone. Spotting illness early is mostly about noticing when something changes from their normal, and knowing which changes can wait a day and which cannot.

How to Tell if Your Dog Is Sick — The Short Answer

The earliest sign of illness is usually a change in routine behaviour, not a dramatic symptom. Watch for:

• Eating less, eating more, or suddenly becoming fussy
• Drinking noticeably more or less water
• Less energy, sleeping more, or reluctance to walk or play
• Hiding, withdrawing, or becoming unusually clingy
• Vomiting, diarrhea, constipation, or accidents in the house
• Coughing, sneezing, or breathing faster at rest
• Limping, stiffness, or trouble getting comfortable
• Changes in their coat, skin, eyes, ears, gums or smell

One small change for a few hours is often nothing. A change that lasts more than a day, or several small changes together, deserves a call to your vet.

The Everyday Signs Worth Watching

Appetite and thirst

A skipped meal in a healthy adult dog on a hot day is rarely a concern. A dog who turns down food for more than a day, or a normally food-obsessed dog who suddenly walks away from dinner, is telling you something.

Thirst matters just as much. A dog who is drinking and urinating a lot more than usual may have a problem such as diabetes, kidney disease or a hormone condition, and it is worth a vet visit even if they otherwise seem fine. If you are unsure what normal intake looks like for your dog, our guide to how much food to feed your dog is a useful baseline.

Energy and behaviour

This is where you have the edge over any vet. Is your dog slower to get up? Skipping the zoomies? No longer bringing you a toy, meeting you at the door, or following you from room to room?

Behaviour changes can also look like "bad" behaviour — growling when touched, snapping, restlessness at night, or house-training accidents. These are frequently signs of pain or discomfort, not a sudden attitude problem. Anxiety can look similar too, which we cover in our guide to dog anxiety.

Toileting

Check what comes out. Diarrhea, very hard stools, blood or mucus, black tarry stool, straining, or needing to go far more often are all worth noting. A single soft stool after a new treat is usually nothing; two days of diarrhea is not. For tummy troubles after a scavenging incident, see our guide to canine food poisoning.

Weight and body shape

Slow weight loss is easy to miss in a dog you see every day. Run your hands over their ribs, spine and hips once a week. If bones feel more prominent than they used to, or their waist has changed, weigh them. Unexplained weight loss is covered in more detail in our guide to a dog losing weight.

Simple Checks You Can Do at Home

These take a few minutes, and doing them when your dog is well gives you a baseline to compare against when something seems off.

Temperature

According to VCA Animal Hospitals, a normal body temperature for dogs is 100.0°F to 102.5°F (37.7°C to 39.2°C). VCA advises taking your dog to the vet if their temperature rises above 104°F (40.0°C) or falls below 99°F (37.2°C).

A warm or dry nose does not tell you anything reliable. The most accurate home reading is with a digital thermometer used rectally, with the tip lubricated with petroleum jelly. Keep a thermometer just for your dog.

Resting breathing rate

Count your dog's breaths while they are asleep or resting calmly — one rise and fall of the chest is one breath. Count for 30 seconds and double it.

VCA's guide to home breathing rate evaluation says a normal resting or sleeping rate is 15 to 30 breaths per minute. Rates consistently above 30 at rest are considered abnormal and can be an early clue to heart failure. If you get a high count, recount a few times over the next couple of hours, and call your vet if it stays up.

This check is especially worth learning for older dogs and breeds prone to heart disease. The Tufts Cummings School cardiology team recommends home monitoring of sleeping breathing rate for dogs with heart disease.

Gums

Lift your dog's lip. Healthy gums in most dogs are moist and pink (some breeds have naturally dark pigment). Pale, white, blue-grey, bright red or yellow gums, or gums that feel dry and tacky, need attention.

A quick nose-to-tail look

• Eyes: discharge, cloudiness, squinting or redness
• Ears: smell, redness, discharge, head shaking
• Skin and coat: new lumps, hair loss, scabs, constant scratching or licking
• Belly: swelling, or flinching when gently pressed
• Legs and paws: limping, swelling, licking one paw

When to Call the Vet Right Away

Some signs cannot wait for a regular appointment. Go to your vet or an emergency clinic immediately for:

• Difficulty breathing, noisy or laboured breathing, or blue or very pale gums
• Collapse, fainting, or a seizure
• A swollen, tight belly with retching that brings nothing up — VCA describes gastric dilatation and volvulus (bloat) as one of the most serious emergencies in dogs, often starting with restlessness after a meal and trying to vomit
• Straining to urinate with little or nothing coming out
• Heavy bleeding, or bleeding that will not stop
• Suspected poisoning — call ASPCA Animal Poison Control at (888) 426-4435 if you cannot reach your vet
• Temperature above 104°F or below 99°F
• Repeated vomiting or diarrhea, especially with blood, or in a puppy or senior dog
• Signs of severe pain — crying out, trembling, refusing to move

When to Book a Regular Appointment

Call for a visit in the next day or two for:

• Not eating for more than a day, or drinking far more than usual
• Low energy lasting more than a day or two
• Mild vomiting or diarrhea that has not settled within 24–48 hours
• A new cough, a limp, or a lump
• Gradual weight loss, or changes in coat and skin
• Any behaviour change that does not have an obvious cause

When you call, have notes ready: what you noticed, when it started, whether it is getting better or worse, and anything your dog might have eaten. Your temperature and breathing counts are genuinely useful here.

What This Means for Different Dogs

Puppies have fewer reserves and can go downhill quickly with vomiting or diarrhea. Call sooner rather than later.

Senior dogs often show illness very subtly — a little more sleep, a slower walk, a changed appetite — and those shifts are easy to dismiss as "just getting old". Vets recommend more frequent checkups for older dogs for this reason; our guide to pet wellness plans covers how often. For a dog with a serious condition, a structured quality of life scale can help you track changes.

Stoic breeds and working dogs may keep going despite real pain. Watch for small signs like reluctance to jump in the car.

Practical Takeaways

• Know your dog's normal — appetite, thirst, energy, toileting, breathing — so changes stand out.
• Normal temperature is 100.0–102.5°F; normal resting breathing is 15–30 breaths per minute.
• One small change is usually nothing. A change lasting over a day, or several together, is worth a call.
• Breathing trouble, collapse, a swollen belly with retching, or suspected poisoning are emergencies.
• When in doubt, call. Your vet would always rather hear from you early.

The best early-warning system is a steady daily routine, because it makes changes obvious. If you are still building that routine, our guide to taking care of a dog is a good place to start.