Noticing a change in body odor when someone is unwell is a common human experience. This perception is a genuine biological signal, not a coincidence. When fighting an infection or struggling with a metabolic disorder, the body releases distinct chemical compounds. These shifts in internal chemistry reflect the underlying biological state, effectively broadcasting a “scent of sickness.”
How Metabolic Changes Create Illness Odors
A sick body smells different because disease alters cellular metabolism. Metabolism, the sum of chemical reactions within cells, generates hundreds of gaseous byproducts known as Volatile Organic Compounds (VOCs). These compounds have a high vapor pressure, meaning they easily evaporate into the air at body temperature, making them detectable by smell.
When disease strikes, metabolic pathways change, altering the type and concentration of VOCs produced. Inflammation and oxidative stress, common responses to infection, can lead to the production of volatile compounds like hydrocarbons, alkanes, and aldehydes. These disease-specific VOCs are released from the body through breath, sweat, and urine.
The composition of these excreted VOCs acts as a unique chemical signature, or a “volatome,” reflecting the body’s internal condition. Microorganisms, such as bacteria and viruses, also produce their own VOCs as part of their metabolism, further contributing to the distinct odors associated with infectious diseases.
Distinct Smells Associated with Specific Conditions
Certain diseases produce recognizable odors due to the accumulation of specific metabolic byproducts. The most well-known example is the sweet or fruity scent on the breath of an individual experiencing diabetic ketoacidosis (DKA). DKA is a serious complication where the body breaks down fat for energy, producing an excess of acidic compounds called ketones. The main volatile ketone responsible for this fruity smell is acetone, which is expelled through the lungs.
Another distinct odor is associated with advanced kidney or liver disease, where the body struggles to eliminate toxic waste products. Kidney failure, for instance, leads to a buildup of urea, which breaks down into ammonia, resulting in a urine-like or fishy smell on the breath and skin.
Inborn errors of metabolism, which are genetic disorders, can also produce strong odors. For example, the rare condition maple syrup urine disease causes the urine to smell distinctly like maple syrup due to the inability to break down certain amino acids. Even bacterial infections have characteristic scents; Pseudomonas aeruginosa infections, often found in wounds, can give off a sweet odor described as grapes or tortillas due to the release of specific microbial VOCs.
The Future of Scent-Based Diagnosis
The body’s ability to broadcast disease through odor is moving from anecdotal observation to a serious area of medical research. Scientists are working to harness this phenomenon to create non-invasive, rapid diagnostic tools. This research focuses on detecting disease-specific VOCs emitted before other symptoms become apparent.
Detection Dogs
One approach involves specialized, highly trained detection dogs, whose olfactory sensitivity is far greater than humans. These animals can be trained to identify the subtle scent profiles of conditions like cancer with high accuracy by analyzing breath or urine samples.
Electronic Noses (E-Noses)
The second major avenue of research is the development of electronic noses, or e-noses. These are sophisticated sensor arrays designed to mimic the canine sense of smell. E-noses use machine learning algorithms to analyze the complex patterns of VOCs in samples, such as breath or urine, to identify the chemical signature of a disease. While current technology faces challenges regarding portability and consistency, e-noses offer the potential for a scalable, quick, and objective screening method. The goal is to integrate these scent detection devices into clinical practice, offering a new frontier in early disease detection and monitoring.