Why People Smell When They’re Sick

Sick people stink. That’s not just an insult, but a scientific reality. Different diseases and illnesses release a range of smells and result in a range of responses, some more compassionate and some more self-protective. “Humans have pretty good noses, and there is research to suggest that people who are sick, or are about to get sick, smell differently than people who are healthy,” says Dr. Christopher Dietz, a physician and Medical Director for MedExpress. So what does sickness smell like?

When people get sick they secrete different scents because their immune systems are in overdrive. This is typically emitted through bad breath, stinky urine, and odorous sweat. The ability to smell sicknesses is well-documented in animals, and dogs can reportedly smell cancer. Humans are capable of smelling sickness to varying degrees, but scientists broadly suspect that bad smells can signal a need for compassion and kindness, or initiate a disgust reaction that keeps us away from contagion.

Different diseases are marked by different odors. “Yellow fever is said to smell like a butcher’s shop. Typhoid fever can smell like baked bread,” Dietz says. Strep throat, sinus infections, colds, and other upper respiratory illnesses, on the other hand, smell more like bad breath, because infected mucus drains to the back of the throat and collects there. These mild illnesses make it harder to breathe out of the nose as well, which leads to dry mouth, a common cause of bad breath.

Men, who generally have a weaker sense of smell than women, may be worse at identifying sick smell. It’s possible that this difference in olfactory abilities may be a evolutionary result of men being less risk-averse in general. So it may be better to defer to mothers when it comes to who stinks, and not take it personally. They’re likely coming from a place of concern and empathy — unless it’s really, really bad. Then they likely just want to get away unscathed.

“When we’re healthy and we smell something unpleasant, we’re likely to avoid it,” Dietz says. “Which, in this case, helps keep us away from germs that can cause sickness.”