Dr Emer Duffy is a post-doctoral researcher at Insight, the Science Foundation Ireland centre for data analytics at DCU. In this interview she talks about what natural odours reveal about our health and why we should be ‘rewilding’ our skin.
We’re used to the idea of having conditions diagnosed by eye but not necessarily by smell.
Humans continuously release chemicals into the air by breath and through the skin. Many of these chemicals are released as gases, and this complex mixture of gases is often referred to as human odour.
It is thought that each human has a unique odour as a product of their own genetic make-up and diverse skin flora composition. Our lifestyle, particularly our diet, can actively influence body odour, for example alcohol and some foods (eg garlic or spices) are secreted through the pores in our skin.
Many diseases are associated with changes in our internal metabolism. These changes in body chemistry can result in subtle changes in body odour. The idea that body odour could be linked to health has been around for centuries. The ancient Greek and Chinese healers used to use odour to diagnose infectious diseases like tuberculosis by smelling a patient’s exhaled breath. More recent examples include the fruity smell of ketones in the exhaled breath of patients with diabetic ketoacidosis and the fishy smell of advanced liver disease.
There are already examples of skin odours being linked to diseases too, such as the unique odour associated with the sweat of people with chronic schizophrenia or the sebum of people with Parkinson’s disease.
There is growing interest in identifying specific markers for different diseases in both breath and skin emissions. This research could help to inform development of new tools for diagnostics or health monitoring.
Recent research has also uncovered the potential to monitor emotional states via exhaled chemicals in breath. A team of researchers in Germany found that specific events during a movie (eg suspense, comedy) caused changes in the emission of specific chemicals from the audience in the cinema, which opens up new opportunities for odour analysis in psychological research.
You’ve talked about the importance of ‘rewilding’ our skin. What do you mean by this?
‘Rewilding the skin’ refers to a new trend in probiotic skincare products. Probiotics are generally taken in capsule form to maintain a healthy gut, a trend that has been motivated by the growing body of research on the human gut microbiome (the array of bacteria and other microorganisms living within our digestive tract). This research has highlighted the important role that bacteria in our intestines play in our digestive health.
Scientists recently discovered that the skin has a specialised microbiome as well. Now many cosmetics developers are attempting to harness the relationship between bacteria and healthy skin. They are creating new products that contain strains of helpful bacteria that occur on healthy skin (probiotics) and prebiotics (food for bacteria). These new products aim to protect and nurture skin by keeping the skin’s resident bacteria in balance. They claim a multitude of benefits from delivering healthier more radiant skin, to treating conditions like acne and body odour.
Scientists are still working to understand the human microbiome and its important role in our health. This is a complex topic that is still the subject of ongoing research.
How does your research work in practice?
I’m working with Assoc. Prof. Aoife Morrin at Insight on the development of sensors to track health via skin gases. Skin gases are released from skin gland secretions (sweat and sebum) and from bacterial activity on these secretions. Many skin gases are released in small amounts, typically at levels below those detected by the human nose. This makes the sample collection step important in my research – to ensure that I collect enough of the gases from skin to be able to identify and measure them in the lab. This work is supporting the development of new sensors in our group.
I collect skin gas samples by placing a small wearable device on the skin for a few minutes. This device contains a polymer material that acts like a sponge to collect the gases coming from the skin. Samples are then analysed in the lab using tools to separate all of the individual component gases. These gases are identified based on matching their properties with a database. Data processing is one of the more time-consuming parts of my research due to the complexity and variety of chemicals present in each skin gas sample.
As a project reliant on data, what kinds of variables are you looking at?
I am interested in understanding the influence of both endogenous (coming from processes within the body) and environmental variables on the mixture of gases released from the skin. These include variables like gender, skin gland distribution, skin flora, personal care product usage and skin health.
My research has shown that gases detected can vary widely depending on the skin site under investigation (eg arms or feet). This variation is due to the distribution of different types of glands and bacteria across the surface of our skin. For instance, some bacteria on feet can break down sweat to release isovaleric acid, which is one of the major components of foot odour.
I also see external contributions (such as those from cosmetics and our environment) mixed with the gases derived from our glands and skin flora. I often see differences between males and females, with female skin exhibiting a greater influence from cosmetics (such as perfumes or moisturisers).
My research has also established that skin gases can change when the skin barrier becomes damaged. The skin barrier refers to the outermost layer of skin which helps protect us from environmental irritants and pathogens and holds in moisture, preventing skin from drying out.
A strong skin barrier is one of the most important aspects of skin health. Some chronic skin diseases, such as eczema or psoriasis, are associated with skin barrier dysfunction, where normally smooth and supple skin becomes dry, irritated, inflamed and susceptible to infection.
What kind of applications do you see your work having?
There is growing interest in identifying specific markers for different diseases in both breath and skin emissions for applications in non-invasive diagnostics or health monitoring.
My work on skin gases could improve our understanding of skin barrier function and support the development of sensors to track skin health status in the future.
A wearable sensor could alert an individual to a change in skin barrier function, for example, so that they can act early to manage their skin health proactively. I’m also developing low-cost sensors for measuring indoor air pollution as part of my MSCA Fellowship in Insight.
I’m working with Prof Alan Smeaton and the Media Analytics Group at Insight to couple the sensors with smart phone technology to understand the impact humans have on indoor air quality (eg through common activities like cooking and cleaning).
My research on skin gases could also be applied during cosmetic product development to understand the modulation of body odour by fragrances or topical probiotics.
There are many other application areas emerging for human odour research. These include understanding host-finding signals for mosquitoes – why mosquitoes prefer to bite certain people over others – as it’s thought that certain gases released from skin and skin flora play a part in attracting mosquitoes.
Scientists are also working to develop odour detection tools for search and rescue operations, which could enable emergency services to locate lost people after a disaster using odour as a marker of human presence.
You are an MSCA fellow. Can you tell us what that entails?
I was awarded a two-year Marie Skłodowska-Curie Actions (MSCA) Individual Fellowship to pursue my research on indoor air pollution at the Insight Centre in DCU.
The MSCA Individual Fellowships are one of the actions through which the European Commission supports experienced researchers. These fellowships are based on the principle of mobility – you receive funding on the condition that you move from one country to another to acquire new knowledge and develop your research career.
My MSCA fellowship supported my return to Ireland after completing my PhD in Australia. The Fellowship is providing me with great opportunities to develop new skills and gain a variety of experience through my research and participation in training workshops, international conferences and interdisciplinary collaborations.