CAN YOU SMELL A DISEASE? EXPLORING THE LINK BETWEEN ODOR AND SICKNESS

Medically Reviewed by Dr. Rae Osborn, Ph.D., July 30, 2024

Have you ever wondered if you can smell a disease? It may sound like a strange question, yet there is actually a fascinating connection between smell and sickness. Throughout history, people have used their sense of smell to detect and diagnose various diseases, from the plague to tuberculosis. You might be wondering how this works if you can smell sickness, and if so, what does sickness smell like?

In this blog post, we will explore the intriguing link between odor and disease and how it can be utilized for early diagnosis and prevention. We will also look at some of the diseases that have distinctive odors and how they can be detected by humans, animals, and machines.

The Role of Smell in Disease Detection

The smell is one of the most primitive and powerful senses that humans have. It is closely linked to our emotions, memories, and behaviors. It also plays a vital role in our physiology, as it helps us to detect and avoid potential threats, such as spoiled food, toxic substances, or predators.

As it turns out, we are more than capable of smelling sickness, and this does in fact, allow us to know when someone is not well. Some people have such an advanced sense of smell that it helps them detect and diagnose diseases, both in themselves and in others. The reason we can smell infection, tell when someone is sick from their body odor, or sense “sick breath” is because many diseases alter the chemical composition of our body fluids. These changes produce volatile organic compounds (VOCs), which are small molecules that can evaporate and diffuse into the air, creating a characteristic odor.

Some of these VOCs are specific to certain diseases and can be used as biomarkers for diagnosis. For example, when the body breaks down fat for energy, it produces acetone, a volatile organic compound that gives a fruity smell to the breath of people with diabetes. Other VOCs are more general and can indicate inflammation, infection, or stress.

The ability to detect and identify these VOCs varies from person to person, depending on their genetic makeup, environmental exposure, and training. Some people have a more sensitive or refined sense of smell than others and can distinguish subtle differences in odors. Some people may also develop an association between certain smells and diseases based on their personal or professional experience.

One of the most remarkable examples of this is the case of Joy Milne, a Scottish woman who can smell Parkinson’s disease before it is diagnosed. She noticed that her husband, who later developed the disease, had a distinct musky odor that she could not find in anyone else. She later discovered that she could identify other people with Parkinson’s disease by their smell and even predict who would develop the disease in the future. Her ability has been confirmed by scientific studies, and she is now working with researchers to help them find the VOCs that are responsible for the Parkinson’s odor.

Another example of the role of smell in disease detection is the use of odor-detection dogs in medical settings. Dogs have a much more sensitive and sophisticated sense of smell than humans and can be trained to recognize and alert specific odors. They can also scan large numbers of samples or people in a short time and provide a non-invasive and cost-effective method of screening.

Odor detection dogs have been used to detect various diseases, such as cancer, diabetes, malaria, and COVID-19.^[1] They can detect these diseases by smelling samples of breath, urine, sweat, or saliva and indicating a positive or negative result by sitting, barking, or pawing. Studies have shown that dogs can achieve high levels of accuracy and reliability in detecting these diseases and can even outperform some laboratory tests.

8+ Health Conditions Associated with Distinctive Odors

There are many body odors that indicate illness and many diseases that have distinctive odors, either because they produce specific VOCs or because they have an impact on the regular functioning of the organs or systems. Here are some of the most common diseases that are associated with distinctive smells and what they smell like:

Diabetes

Blood sugar regulation is impacted by diabetes. When the body does not have enough insulin to use glucose for energy, it resorts to burning fat instead. This produces ketones, which are a type of VOC that give a fruity or acetone-like smell to the breath^[2]. This condition is known as diabetic ketoacidosis and can be life-threatening if not treated promptly. People with diabetes may also have a sweet or fruity smell in their urine due to the excess glucose that is excreted by the kidneys.

Kidney disease

Kidney disease is a condition that impairs the kidneys' ability to remove waste products and extra fluid from the blood. When the kidneys are damaged or diseased, they cannot remove these substances efficiently, and they accumulate in the body. Urea, a waste product that is typically expelled in urine, may accumulate as a result of this. Urea can break down into ammonia, which is a VOC that gives a strong or foul smell to the urine. People with kidney disease may also have a fishy or ammonia-like smell to their breath due to the urea that is transferred to the lungs and exhaled.^[3]

Liver disease

Liver disease is a condition that affects the function of the liver, which is responsible for metabolizing and detoxifying various substances in the body. When the liver is damaged or diseased, it cannot perform these functions properly, and some of these substances can accumulate in the body. A few of these include bilirubin, mercaptan, and dimethyl disulfide, all of which contribute to what is known as ‘foetor hepaticus’ or cirrhosis body odor. This causes the urine or breath to have a musty, sweet, or metallic smell that may occasionally also reek of garlic or rotten eggs.^[4] Further studies have linked limonene, methanol, and 2-pentanone to cirrhosis body odor.^[5]

Cancer

Cancer leads to abnormal cell growth and division in the body. Cancer can affect any part of the body and can produce different odors depending on the type and location of the tumor. Dogs and electronic noses are able to detect these odors, which are brought on by the volatile organic compounds (VOCs) released by tumor cells^[6]. Some of the odors that have been associated with cancer are:

• Lung cancer: Lung cancer affects the lungs and can cause symptoms such as chest pain, coughing, and shortness of breath. Lung cancer can also produce a distinctive odor in the breath, which has been described as sweet, musty, or moldy. Apparently, there are 21 VOCs (and counting) that have been associated with the smell of lung cancer.^[7]
• Breast cancer: Breast cancer affects the breast tissue and can cause symptoms such as lumps, pain, or discharge. Breast cancer can also produce a distinctive odor in the sweat, which has been described as fruity, floral, or spicy. Some breast cancer patients also have an altered sense of smell as a result of these compounds, which they may smell due to a buildup in their systems and which no one else may smell.
• Skin cancer: Skin cancer affects the skin and can cause symptoms such as changes in the shape, color, or size of a mole or lesion. Skin cancer can also produce a distinctive odor in the skin, which has been described as rancid, sour, or burnt. This odor is caused by the VOCs that are produced by the tumor cells and can be detected by dogs and electronic noses.

Odors associated with cancer can also result from the treatment that a patient undergoes^[8]. For instance, chemotherapy can cause changes in both the color and odor of a patient’s urine.

Gout

A painful inflammation of the joints, generally in the big toe, is caused by gout, a form of arthritis. In gout, the excess uric acid that builds up in the joints as crystals can also accumulate in the kidneys, imparting a strong odor to the urine^[9]. Urine naturally excretes uric acid, a waste product that can break down into ammonia when it builds up, and has an overpowering or unpleasant smell.

Menopause

Menopause is the stage of life when a woman’s ovaries produce less estrogen and progesterone, and her periods stop. Menopause can cause changes in body odor due to the hormonal fluctuations that affect sweat production, saliva flow, and vaginal flora. According to experts, this can be due to the drop in estrogen and the relatively higher degree of testosterone present in its place^[10]. Some women may experience an intensification of their natural scent, while others may develop a fishy, fruity, acidic, or musty smell, depending on the type and location of the odor.

Hyperthyroidism

Hyperthyroidism is a condition in which the thyroid gland produces and releases too much thyroid hormone, which regulates the metabolism and other body functions. Hyperthyroidism can cause excessive sweating, which can lead to an increase in body odor, especially in the armpits, groin, and feet. Hyperthyroidism can also cause a fruity or acetone-like smell in the breath due to the breakdown of fat for energy, which produces ketones, a type of VOC that gives a sweet or sour smell.

Infections

Infections are a very common source of body odor and often lead to bad breath, foul-smelling skin, and sweat. Common infections and their associated smells are described below:

• Staphylococcus infections have been described as smelling like dirty sneakers, stale beer, or old cheese. This odor is caused by the production of isovaleric acid, a volatile fatty acid that is released by the bacteria as they break down amino acids in sweat and sebum.^[11]
• Streptococcus infections may strangely smell like butter, butterscotch, caramel, or cake. This odor is caused by the production of diacetyl, a compound that is known for its buttery aroma and is used as a flavoring agent in some foods.
• E. coli can cause urine to smell like rotten fruit, vinegar, or sour milk. This odor is caused by the production of indole, a compound that is formed when the bacterium breaks down tryptophan, an amino acid.^[12]
• Helicobacter pylori can cause really bad breath, described as rotten eggs, sulfur, or sewage. This odor is caused by the production of hydrogen sulfide, a gas that is formed when the bacterium reduces sulfur-containing compounds in the stomach.^[13]
• Candida infections usually do not have a strong odor, but some people may notice a mild yeasty smell, similar to bread or beer. This smell is caused by the production of ethanol and acetaldehyde, two alcohols that are formed by the yeast as they ferment sugars.

Utilizing Odor Detection for Early Disease Diagnosis

The ability to detect and diagnose diseases by their odors has many potential benefits, especially for early detection and prevention. Early detection can improve the chances of survival and recovery and reduce the need for invasive and expensive treatments. Prevention can reduce the risk of developing or spreading diseases and improve the quality of life and well-being.

One of the ways to utilize odor detection for early disease diagnosis is to develop electronic noses, which are devices that can mimic the function of the human or animal nose. Electronic noses consist of sensors that can detect and identify VOCs and algorithms that can analyze and interpret the data. Electronic noses can be designed to detect specific diseases or to screen for a range of diseases, depending on the application.^[14]

Electronic noses have been developed and tested for various diseases, such as cancer, diabetes, tuberculosis, and COVID-19.^[15] They have shown promising results in terms of accuracy, sensitivity, and specificity and have some advantages over other methods of diagnosis, such as speed, portability, and affordability. However, they also face some challenges, such as standardization, validation, and regulation.

Another way to utilize odor detection for early disease diagnosis is to integrate it into clinical settings, where it can complement or supplement other methods of diagnosis. For example, odor detection dogs can be used to screen large numbers of people or samples for diseases, such as malaria or COVID-19, and refer them to further testing if needed. This can save time, resources, and lives, especially in remote or low-resource areas.

However, there are also some ethical considerations and challenges that need to be addressed before odor detection can be widely used for early disease diagnosis. Some of these are:

• Privacy and consent: Odor detection involves the collection and analysis of personal and sensitive information, such as body fluids, breath, or body odor. This raises questions about who owns, accesses, and controls this information and how it is protected and used. It also requires the consent of the individuals who are being tested and the respect for their dignity and autonomy.
• Social and cultural implications: Odor detection may have social and cultural implications, such as stigma, discrimination, or prejudice, based on the association of certain smells with certain diseases or groups of people. This may affect the acceptance and adoption of odor detection and the trust and confidence in the results. It may also affect the psychological and emotional impact of odor detection and the coping and support mechanisms for the individuals who are tested.
• Scientific and technical challenges: Odor detection faces some scientific and technical challenges, such as the complexity and variability of VOCs, the influence of environmental and physiological factors, and the lack of standardized and validated methods and protocols. These challenges may affect the reliability and reproducibility of odor detection and the comparability and compatibility of different devices and systems.

Future Directions in Odor-Based Disease Detection

Despite the challenges, odor detection has great potential for early disease diagnosis, and there are many future directions that can be explored to improve and expand its applications. Some of these are:

• Advancements in sensor technology and data analysis: Sensor technology and data analysis are the core components of electronic noses, and they can be improved by using novel materials, designs, and algorithms. For example, nanomaterials, such as graphene and carbon nanotubes, can be used to enhance the sensitivity and selectivity of sensors, and machine learning and artificial intelligence can be used to enhance the accuracy and efficiency of data analysis.^[16]
• Integration of odor detection into personalized medicine: Personalized medicine is an approach that tailors medical care to the individual characteristics and needs of each patient, such as their genetic, environmental, and lifestyle factors. Odor detection can be integrated into personalized medicine by using it to monitor and track the changes in the VOCs of each patient and provide feedback and guidance for prevention and treatment.
• Expanding the range of detectable diseases through research: Research is essential to discover and validate new VOCs and biomarkers for different diseases, and to understand the mechanisms and pathways behind them. Research can also help identify and address the factors that affect the performance and outcomes of odor detection and evaluate and compare its effectiveness and feasibility with other methods of diagnosis.

Conclusion

Odor detection is a fascinating and promising field that explores the link between smell and sickness. It has many potential benefits for early disease diagnosis and prevention, and it can be utilized by humans, animals, and machines. However, it also faces some ethical, social, cultural, scientific, and technical challenges that need to be addressed before it can be widely adopted and applied. Odor detection is still in its infancy, but it has a bright future ahead.

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