Dogs share our homes, routines, and sometimes even our health problems. Many health conditions dogs and humans share involve the same organs, hormones, joints, or immune responses. The symptoms and treatments are not always identical, but the similarities can be striking.
That does not mean most of these conditions pass between people and dogs. Diabetes, arthritis, epilepsy, and cancer are not contagious. Dogs and humans develop them independently because our bodies rely on many of the same biological processes.
Learning about these similarities can help owners recognize when something has changed. However, recognizing a possible warning sign is not the same as making a diagnosis. A veterinarian must determine what is actually happening and recommend the appropriate treatment.
1. Diabetes
Diabetes develops when the body cannot properly regulate glucose in the bloodstream. Both dogs and people may develop the disease, although the most common forms and underlying causes differ between species.
A diabetic dog may drink much more than usual and need frequent trips outside. Other signs can include increased appetite, weight loss, fatigue, cloudy eyes, and recurring infections. Because several illnesses cause similar symptoms, blood and urine testing are needed.
Most dogs with diabetes require insulin injections, carefully timed meals, and regular monitoring. Insulin should never be adjusted merely because a dog is large or small. The veterinarian determines the dosage by considering the dog’s weight, glucose response, diet, activity, and overall health.
2. Arthritis
Anyone who has struggled to rise from a chair with aching knees may recognize some of the difficulties an arthritic dog experiences. Osteoarthritis gradually damages joints, causing inflammation, stiffness, reduced movement, and chronic pain.
Dogs do not always announce their discomfort with a dramatic limp. One may hesitate before climbing stairs, take longer to stand, avoid slippery floors, or stop jumping onto a favorite chair. Irritability and reduced interest in play may also reflect pain.
Veterinarians use the dog’s history, physical examination, and sometimes X-rays to evaluate affected joints. Treatment may include weight management, appropriate exercise, rehabilitation, pain medication, and other therapies selected for the individual dog.
Owners can learn more about recognizing discomfort in Understanding Canine Pain: Types, Causes, and Safe Treatment Options.
3. Epilepsy and Seizure Disorders
Epilepsy can cause recurring seizures in dogs as well as people. During a generalized seizure, a dog may fall, stiffen, paddle the legs, drool, or lose control of the bladder or bowels. Confusion, temporary blindness, hunger, or restlessness may follow.
Not every seizure means that a dog has epilepsy. Toxins, abnormal blood sugar, liver disease, infections, head injuries, and structural brain disorders can also cause seizures. Veterinarians often use bloodwork and neurological findings to investigate these possibilities.
Some dogs need long-term anticonvulsant medication, while others may initially be monitored. The decision depends on seizure frequency, severity, duration, and the dog’s test results. A seizure lasting several minutes or repeated seizures without recovery require emergency veterinary care.
4. Cancer
Cancer is not one disease but a large group of diseases involving uncontrolled cell growth. It can affect nearly any part of a human or canine body, including the skin, bones, blood, lymphatic system, and internal organs.
Possible warning signs include a new or changing lump, unexplained weight loss, persistent swelling, abnormal bleeding, ongoing pain, or a sore that does not heal. Changes in appetite, energy, breathing, urination, or bowel habits may also warrant investigation.
Fortunately, every lump is not cancerous. A veterinarian may examine a sample of cells, perform a biopsy, order bloodwork, or use diagnostic imaging to identify the problem. Treatment may involve surgery, chemotherapy, radiation, immunotherapy, comfort care, or a combination of approaches.
Age, genetics, environment, and cancer type all influence risk. Certain breeds have greater susceptibility to specific cancers, but no breed is completely protected.
5. Obesity
Extra weight can creep onto dogs and people so gradually that family members stop noticing it. A few additional treats, larger portions, and less activity may not seem important individually. Over time, however, the difference can become substantial.
Obesity increases strain on the joints and can complicate diabetes, breathing problems, and cardiovascular disease. It may also reduce mobility and make warm weather more difficult for a dog to tolerate.
Veterinarians usually evaluate more than the number on a scale. They consider body shape, the waist, abdominal tuck, and how easily the ribs can be felt. This body-condition assessment helps determine whether weight loss is appropriate.
A safe plan balances nutrition, portion control, physical ability, and any medical limitations. Dramatic food restriction can deprive a dog of necessary nutrients, so weight-loss goals should be developed with veterinary guidance. The story of one dog’s weight struggle appears in Dog on a Diet to Save His Life.
6. Allergies
Dogs and people can react to pollen, dust mites, molds, foods, insect bites, and other substances. However, canine allergies often appear through the skin rather than primarily through sneezing and watery eyes.
An affected dog may lick their paws, rub their face, scratch constantly, or develop red skin and recurring ear infections. Some food reactions can also cause vomiting, diarrhea, or frequent bowel movements.
Diagnosing allergies requires patience because parasites, infections, and other skin diseases can cause nearly identical symptoms. Environmental allergy testing may help veterinarians identify allergens when immunotherapy is being considered.
Suspected food allergies require a carefully controlled elimination diet followed by a food challenge. Commercial blood, saliva, and hair tests do not reliably diagnose canine food allergies. Every treat, flavored medication, and chew must be considered during a legitimate diet trial.
7. Heart Disease
The heart works continuously to circulate oxygen and nutrients throughout the body. When disease interferes with that work, dogs and humans may experience fatigue, reduced stamina, breathing difficulties, or fluid accumulation.
Warning signs in dogs can include coughing, rapid breathing at rest, fainting, weakness, or reluctance to exercise. Some dogs have no obvious symptoms when a veterinarian first detects an abnormal heart sound.
Smaller dogs more commonly develop degenerative disease of the mitral valve. Certain larger breeds face an increased risk of dilated cardiomyopathy, which weakens the heart muscle. These patterns are useful, but an individual dog cannot be diagnosed according to size or breed alone.
Chest X-rays, electrocardiograms, blood pressure measurements, and echocardiograms may be used during an evaluation. Treatment depends on the diagnosis and may include medication, activity adjustments, dietary guidance, and regular monitoring.
8. Lyme Disease
Lyme disease differs from most conditions on this list because it is caused by bacteria transmitted through infected ticks. People and dogs can both become infected after a tick bite, particularly in regions where blacklegged ticks are established.
Dogs do not ordinarily give Lyme disease directly to their owners. However, an unprotected dog can carry ticks into a home or yard, where those ticks may later attach to people or other animals.
Many exposed dogs never become visibly ill. Those that do may develop fever, swollen joints, shifting leg lameness, reduced appetite, or lethargy. Rarely, Lyme disease contributes to serious kidney complications.
A positive antibody test shows that a dog has been exposed, but it does not always prove that Lyme disease is causing the current symptoms. Veterinarians interpret test results alongside examination findings, exposure history, and other laboratory information.
Consistent tick prevention and routine tick checks help protect the entire household. Owners should ask their veterinarian which preventive product and vaccination strategy are appropriate for their dog and location.
9. Depression-Like Behavior
Human clinical depression has specific diagnostic criteria that cannot simply be transferred to dogs. Still, dogs can display withdrawal, reduced interest, low energy, and other changes that resemble depression.
These behaviors sometimes follow the loss of a companion, a move, prolonged isolation, or a major disruption in family life. Dogs form attachments and depend heavily on familiar routines, so significant changes can affect them deeply.
However, a dog that stops playing or begins sleeping more may be experiencing pain or illness rather than grief alone. Thyroid disease, arthritis, sensory decline, medication effects, neurological problems, and many other conditions can alter behavior.
A veterinary examination should come before assuming the problem is emotional. Once medical causes have been addressed, predictable routines, gentle activity, social contact, enrichment, and behavior support may help. Medication may be appropriate in selected cases under professional supervision.
10. Hypothyroidism
The thyroid gland produces hormones that influence metabolism and many other body functions. Hypothyroidism occurs when the gland does not produce enough thyroid hormone. It affects people and is one of the more familiar endocrine disorders seen in dogs.
Dogs may gain weight despite eating a normal amount. They may also become sluggish, seek warm places, develop thinning hair, or experience recurring skin and ear problems. Changes often develop gradually and can be mistaken for ordinary aging.
Diagnosis requires more than a single low thyroid value. Other illnesses and certain medications can suppress thyroid results in dogs without true hypothyroidism. Veterinarians consider the dog’s symptoms, medical history, examination, and a properly interpreted thyroid panel.
Confirmed hypothyroidism is usually managed with lifelong oral thyroid-hormone replacement. Follow-up testing helps the veterinarian determine whether the dosage is producing an appropriate response.
Similar Symptoms Do Not Always Mean the Same Disease
The similarities between human and canine medicine are fascinating, but they can also encourage misleading comparisons. A coughing person and a coughing dog do not necessarily have comparable illnesses. The same is true of weight gain, fatigue, stiffness, seizures, and skin problems.
Dogs also metabolize medications differently from people. A drug commonly found in a household medicine cabinet may be ineffective or dangerously toxic to a pet. Never give a dog human medication unless a veterinarian has specifically directed its use for that dog.
When Your Dog Needs Veterinary Care
Some medical emergencies are unmistakable, but many diseases begin with quieter changes. Owners often notice that something is wrong before they can describe exactly what has changed.
Contact a veterinarian when a dog develops persistent appetite changes, unexplained weight loss, increased thirst, repeated vomiting, breathing difficulty, unusual swelling, ongoing pain, seizures, or a sudden behavioral change. Collapse, severe breathing distress, prolonged seizures, uncontrolled bleeding, and suspected poisoning require immediate care.
Photographs, short videos, and written notes can help document symptoms that appear intermittently. Record when the problem began, how often it occurs, and whether anything seems to trigger it.
What Dogs Can Teach Us About Health
Dogs share much more than our homes. They live in many of the same environments and can develop diseases involving the same organs, immune responses, hormones, and age-related changes.
Studying health across species can help researchers understand disease more completely. This connection is part of the One Health approach, which recognizes that human, animal, and environmental health are closely linked.
For families, the lesson is more personal. Pay attention to subtle changes, maintain preventive care, and seek help when something seems wrong. Dogs cannot explain how they feel, but their bodies and behavior often provide the first clues.
Health & Safety Note: This article is provided for general educational purposes only and is not a substitute for professional veterinary diagnosis, treatment, or emergency care. Every dog is an individual; what works for one may not be appropriate for another’s age, breed, or medical history. Please contact your veterinarian immediately if your dog is sick, injured, in pain, or experiencing sudden behavioral changes. Never delay seeking professional advice because of something you have read online.
Sources: Veterinary information was reviewed using resources from the Merck Veterinary Manual, VCA Animal Hospitals, and the Centers for Disease Control and Prevention’s One Health program.
Editor’s Note: This article was last updated in July 2026 to improve medical accuracy and provide additional information for dog owners.
Photo Credit: All images © Sloan Digital Publishing and licensed stock sources. Used with permission.
