The human sense of smell is powerful, it makes an important and yet often undervalued contribution to our quality of life and wellbeing with a unique link to emotions and memories. Smell dysfunctions or loss (even temporary) gives rise to a range of problems, which can affect personal safety, enjoyment of food, personal hygiene, and can cause serious mental health disorders, including depression, anxiety and social isolation.

In Europe and the USA, around 20% of the general adult population has some form of smell dysfunction and this number rises to 75% for people aged between 70–80 years. The negative effects of smell dysfunctions have in recent years been experienced by a larger global population due to the impact of COVID-19.

Why should we test our olfactory functions?

There is a growing move to facilitate the introduction of personalized medicine, with a focus on the early stage diagnosis of conditions and continuous health monitoring, rather than periodic sampling. Routine smell testing can play a crucial role in this goal by facilitating the early stage diagnosis of neurological conditions including Alzheimer's and Parkinson's disease.

Smell dysfunction can also occur as a result of, for example, head trauma or viral infections. It’s detection through smell testing could be used to facilitate treatments such as smell training, a form of rehabilitation of the sense of smell. Smell training involves repeatedly exposing patients to odor stimuli to help the damaged olfactory nerve repair itself and has been shown to help people improve their sense of smell in a number of peer-reviewed studies published since 2009.

Improved diagnostic technology for smell health and care will allow people to remaining healthier and independent for longer.

How are smell tests currently performed?

Smell threshold tests are analogous to hearing tests, which measure the lowest perceived intensity of a sound, olfactory threshold tests measure the lowest perceived concentration of an odor.

Owing to the high dimensionality of the olfactory stimulus space and the large dynamic range of human smell receptors, a large number of odors of different types and dilutions are often used.

Existing threshold tests, such as the Sniffin’ Sticks test, use multiple felt-tip pens filled with serial odorant dilutions which are manually presented to the patient by a highly specialized nurse.

Why we need a better approach for smell testing?

Today’s approaches for smell testing have a number of limitations, including (i) poor control over the odor stimuli delivery accuracy, (ii) lack of digital performance records for monitoring changes in smell health over time, and (iii) a time-consuming testing paradigm, as odors are manually presented to patients by a specialized nurse. Automated odor delivery devices, such as olfactometer systems, exist but are typically expensive, bulky and lab based, making them difficult to deploy in clinical settings. Miniaturized odor delivery devices have also been commercially developed, however, such low cost miniaturized devices are generally aimed at the entertainment market and lack the performance, features and data collection tools needed for clinical testing.

How advances in digital technology can offer a solution?

To overcome the limitations of existing smell testing solutions, the Sussex University spin-out OWidgets (T/A OW Smell Made Digital), associated with the UCL Department of Computer Science, developed a portable odor delivery device that can deliver 24 odors with high temporal precision. The odor delivery device is much more compact and portable compared to many existing olfactometer designs. It is self-contained and does not require an external air supply. The use of individual odor channels avoids cross-contamination and the removable odorant cartridges can be easily exchanged between experimental sessions. Liquid odors are contained on a cellulose sponge absorber in the odorant cartridges.

The device enables the fast sequencing of odors via digital control over Bluetooth using a mobile application. By harnessing cutting-edge science and proprietary technologies, OW is pioneering a new realm of digitally controlled scent experiences that are both memorable and enriching.

What is the performance of a technology-enabled smell test?

The odour delivery device has been experimentally validated in the lab, through collaborations with Cambridge and UCL Universities, as well as tested on patients with a study at University Hospitals. Lab based studies included validation of the airflow and odour concentration using a flow and gas sensors.

For the study in a clinical setting, groups of patients undertook a standard Sniffin' Sticks smell test and the SMELL-S test which was a self-administered test using a computerized app that guides the subjects through the testing paradigm. The SMELL-RS test (of which SMELL-S is a subset) was developed by Julien Hsieh and Andreas Keller and team at The Rockefeller University, New York. The SMELL-S stimulus is composed of a complex odor mixture with 10 dilutions in a geometric series.

A comparison with a standard Sniffin' Sticks smell test suggests that time savings can be achieved through the automation and removal of human tasks such as capping uncapping the Sniffin' Sticks. The device's digital integration with an app and cloud based ecosystem enables efficient data collection from users, removing the need for laborious manual reporting tasks.

The design provides several advantages for investigating olfactory perception and offers the possibility that patients can one day self-administer smell tests in a range of settings, including at home, allowing smell healthcare services to evolve and become part of a routine practice and self-care culture, that will help establish and co-develop a ‘Culture of smell care’.

Want to hear more?

You can find more information about digital technology on our website https://www.ow-smelldigital.com/ and follow the progress on our X account @o_widgets

You can find further information on associated research efforts on digital smell training on the Smell Care project website: https://www.smell-care.co.uk/