You Can Smell When Someone’s Sick—Here’s How

The curious case of a woman who can smell Parkinson’s reminds us our noses are our first defense against illness.

Joy Milne (right) was able to correctly identify people with Parkinson’s disease based solely on their smell.

I’m sick, and I don’t smell right. I don’t mean that my nose isn’t working—though this cold has me stuffed up. Instead, my own body odor seems somehow different, sour and unfamiliar.

I’m far from the first person to notice this nasty side effect. Scientists have found that dozens of illnesses have a particular smell: Diabetes can make your urine smell like rotten apples, and typhoid turns body odor into the smell of baked bread. Worse, yellow fever apparently makes your skin smell like a butcher’s shop, if you can imagine that.

It’s curious, but not merely a curiosity; some scientists think that if we could identify particular sick smells, we might sniff out diseases that are otherwise hard to detect early, like cancers or brain injuries. Recently, a Scottish woman became famous for her ability to tell whether someone has Parkinson’s disease by smelling their T-shirts.

We marvel at such a skill, but anyone with working olfactory senses could probably learn to recognize various “sick smells.” Humans are very good at detecting illness, says Valerie Curtis, a public health researcher at the London School of Hygiene and Tropical Medicine and author of the book Don’t Look, Don’t Touch, Don’t Eat on the science of disgust.

“Signs of sickness are some of the things people find most disgusting,” Curtis says—think mucus, vomit, or pus. Disgust is our way of avoiding things that could harm us, so “it simply makes good evolutionary sense that we use our noses to notice illness.” (Of course, people sometimes like stinky things, too.)

But why would sick people smell differently in the first place? The key is that our bodies are constantly launching volatile substances into the air. They’re carried in our breath and literally ooze from every pore, and they can vary depending on age, diet, and whether an illness has thrown off some cog in our metabolic machinery. Microbes living in our guts and on our skin also contribute to our signature scent, by breaking down our metabolic by-products into smellier ones.

Basically, you’re a walking factory of smells. And if you start paying attention to them, you might notice when something’s off.

National Geographic

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