The Science Behind Your Body Odor: What It Reveals About You

The Hidden Messages in Body Odour

Whether it's on a busy bus, in a sweaty gym, or on a crowded dancefloor, all of us have experienced an unpleasant whiff of someone's body odour. The pong might have you covering your nose, or reaching for the closest can of deodorant. But if you can bear to sniff it, scientists say the exact aroma can actually divulge a lot about someone. From the unmistakable pong of elevated stress levels, to the stale beer aroma of a tuberculosis infection, your body odour can reveal key clues to your health. And for some 'super-smellers', even complex diseases like early-onset Parkinson's can be detected with a simple sniff.

Dr Bruce Kimball, a smell expert from the Monell Chemical Senses Centre, shared insights into how various diseases can alter bodily odours. He mentioned that there was a time when physicians would commonly sniff patients' urine to detect some conditions. This highlights the long-standing relationship between scent and health diagnosis.

Uncovering Health Clues Through Smell

Rancid beer is one such example. If you've sat next to someone who stinks of rancid beer, it might not just be a sign that they've had a big night on the town. In fact, a strong odour of stale beer is a common sign of a tuberculosis infection. This is because the bacteria which infest the lungs to create the tuberculosis condition produce a strong odour. Since these make their home in the respiratory system, the smell is often strongest on the patient's breath. However, in some cases, a person with tuberculosis will emanate an odour from their skin which has been described as 'wet cardboard' and brine.

Professor Perdita Barran, a smell researcher from Manchester University, explained that we likely evolved the ability to smell this infectious disease as a survival trait. She says: 'The same as we have evolved to smell rotting food, it's easy to understand how we might have retained the ability to diagnose something that's infectious.'

What Your Body Odour Says About You

Here are some examples of what different smells could indicate:

• Pungent sweaty smell: High levels of stress
• Stale beer and wet cardboard: Tuberculosis
• Fishy or urine-like smell: Kidney damage
• Sweet overripe fruit: Type 1 diabetes
• Garlic or spices: Eating too much spicy food
• Musky grease: Parkinson's disease

Fish and Urine: A Warning Sign

If your body odour starts to take on a fishy and 'urine-like' smell, this could be a seriously bad sign. These odours can be a sign of severe kidney disease, which is interfering with your body's ability to process toxins. The kidneys are essentially the body's filtration system, responsible for taking harmful chemicals out of the blood and removing them through urine. If the kidneys aren't working, the chemicals that our bodies would normally expel simply build up in the blood. As we sweat, some of those chemicals leach out onto the skin, where they evaporate and produce an intensely unpleasant smell.

In some rare cases, a fishy smell might also be caused by the condition 'Trimethylaminuria'. This is a genetic condition which leaves the body unable to break down a chemical compound called trimethylamine. This chemical then escapes the body through sweat and produces an odour similar to rotten eggs, fish, or rubbish.

Overripe Fruit: A Sweet Indicator

One of the best-known uses of smell to detect illness is the warning that comes from sweet-smelling breath. Although that might sound pleasant, if someone's breath smells like sugar or they have an odour like an 'old fruit bowl', it's likely a sign that they are seriously ill. A sweet smell is a sure sign of critically low insulin levels in your body, which can be a sign of undiagnosed Type 1 diabetes. When levels of insulin, a hormone which our body needs to turn sugar into energy, get too low, the body starts breaking down fat for energy instead. This process releases chemicals called 'ketones' into your bloodstream, producing an unusually sweet smell.

Professor Barran says: 'That process releases ketones and we humans are good at smelling ketones.' This process also turns the patient's blood acidic, which can be fatal in some cases. 'Paramedics are taught to smell the breath of people who have collapsed in the street and check for a ketone smell, because that's a sign that someone has become hyperglycaemic,' points out Professor Barran.

Pungently Sweaty: Stress and Body Odour

If you've ever had a stressful day at work or had to run for the bus, you might have noticed that your body odour is much worse than normal. This is because stress sweat really does smell worse than normal sweat. Our body is covered with about two to four million sweat glands, of which most are a type of cell called eccrine glands. However, when we become stressed, we start to sweat much more heavily through a second type of gland known as apocrine glands. These are concentrated in hairy areas like our armpits, and produce sweat that is rich in proteins and fatty chemicals called lipids.

Dr Kimball points out: 'Our odour profile is not just a result of our own metabolism. We support millions of microbes, and they can respond to changes in our metabolism too.' When these microbes are suddenly doused in nutrient-rich stress sweat, this triggers a feeding frenzy on your skin. The volatile chemicals released by the bacteria as they feed and multiply are what give stress sweat its pungent stench.

Garlic or Spices: A Simple Explanation

Sometimes, the explanation for someone's body odour is very simple. Foods that contain lots of volatile chemicals can directly influence the smell of someone's sweat. When you eat a lot of onions, garlic, or spices, the chemicals which give these foods their flavour stay in our bodies. Eventually, those chemicals are expelled in the form of sweat, where they evaporate off the skin. So, if you have a particularly fragrant meal, you may be able to smell it for quite a while later.

Greasy Musk: A Sign of Parkinson’s Disease

Although not everyone will be able to detect this smell, it is certainly one to watch out for. A handful of extremely talented 'super-smellers' have the incredible ability to smell Parkinson's disease - even before doctors would be able to diagnose the condition. Perhaps most famously, a 74-year-old retired nurse called Joy Milne amazed scientists with her claim that she could smell Parkinson's disease. In a trial, scientists gave Ms Milne 12 shirts to smell, six of which had recently been worn by Parkinson's patients. Not only did she correctly identify the six Parkinson's patients, but she also identified an additional person who was diagnosed with the condition less than a year later.

According to Ms Milne, the smell of Parkinson's is a musky, greasy odour that clings to clothes and fabric. Professor Barran says: 'The smell of Parkinson's is strongest when a patient's symptoms are least well managed. So that is usually before they are diagnosed or if their medication isn't working.' Ms Milne is able to detect this smell because she has a condition called hereditary hyperosmia, which makes her thousands of times more sensitive to smells than the average person. While Ms Milne's talents are unique, Professor Barran says that many women have reported noticing a sudden change in their partner's odour before they were diagnosed with the condition.