Do Dogs Know When You Are Sick?

One night after returning home from a trip, my whole body ached and felt heavy. I had chills and began to shake uncontrollably. I was coughing to the point of vomiting. Well, it turned out I had caught a bad case of the flu. But during this time a question popped into my head: Do dogs know when you're sick?

My dog (who is usually very independent and likes to sleep by herself in our closet) suddenly became very clingy. For the next week, she slept curled up next to me in bed, with her head resting on my body. She sat in the bathroom every time I took a shower. She refused to go for walks with my husband because she didn't want to leave my side.

When I got worse and had to go to the ER one night, she waited by the door for me until I got home. She even seemed more attuned than my toddler (who was climbing on me while I was sleeping and demanding I chase her around the house) to the fact that I was sick.

It made me wonder if dogs can actually tell when you're sick and, if so, how do they know? I talked to a veterinarian about how dogs can sense illness — and how their behavior changes when they do. Here's what I found out.

Dogs are "keenly attuned" to their humans.

"Many people have stories of how their dog seems to sense when they are not feeling well, and they may not be wrong," Dr. Jerry Klein, chief veterinary officer for the American Kennel Club, told Scary Mommy. "Dogs are keenly attuned and sensitive to their people."

When we're sick, our behaviors, routines, emotions, voices, and even smells can shift — and dogs can pick up on these subtleties.

Dogs know your daily routines.

Dogs thrive on routines and knowing what to expect, from what time you go to bed and wake up to when you walk them and feed them. And when there is a change in these daily habits, they notice.

When you're sick, your routine may go haywire. If you're laying in bed for hours during the day, not eating your usual meals, and not getting outside to walk, your dog will likely pick up that something isn't normal.

Dogs can sense human emotions.

When we're sick, our emotional state is often also affected: We may feel depressed, anxious, or irritated. These emotions can often change our facial expressions. "Dogs have even been found to recognize subtle eye and facial changes in their humans," Klein explained.

One study showed that beyond just facial expressions, dogs can actually recognize human emotions by combining information from different senses. Researchers showed dogs photos of facial expressions and audio clips of voices or barks, and the dogs spent longer looking at the expressions that matched the voices. This cognitive ability "has never previously been observed outside of humans," according to Science Daily. Pretty incredible!

Dogs have an extremely strong sense of smell.

There's a reason your dog is constantly sniffing around their surroundings. Dogs have an "exponentially more powerful" sense of smell than people, Klein said. They have 300 million olfactory receptors in their nose while humans only have 6 million. Illnesses can change a person's odor, and dogs can smell these changes that people often can't.

More recently, people have learned that dogs can be trained to detect viruses (like COVID), bacteria, Parkinson's disease, malaria, and low blood sugar levels in diabetic patients. They can also identify many types of cancer, such as melanoma, colorectal cancer, lung cancer, ovarian cancer, prostate cancer, and breast cancer.

So, how do they smell these diseases? Klein explained that cancer cells and some disease processes produce and release signature odors called volatile organic compounds (VOCs).

"Depending on the disease or type of cancer, dogs may be able to detect VOCs in a person's skin, breath, urine, feces, and sweat," he said.

How does their behavior change when they sense you're sick?

When dogs sense that you are fighting an illness, Klein said it's common behavior for them to cling to you, lick you excessively, and be more protective of you than usual. If a dog senses you are in danger, they may become nervous and repeatedly bark.

Dogs can also be trained to behave in a particular way according to the condition. For example, some seizure assistance dogs are trained to stand next to their owners and catch them as they lose control and fall over.

While the data about how dogs identify illness is relatively new to science and the medical community, "these findings hold huge potential for the future," Klein said.

The biggest takeaway: They are only more proof that dogs are humans' real best friends (as much as I love my toddler).