The world was quick to recognize the loss of smell as a significant symptom of COVID-19 during the pandemic. Even now, nearly four years later, one in five individuals in the UK grapples with a diminished or distorted sense of smell, while one in twenty suffers from anosmia, the total inability to perceive any odors. The prevailing solution for reclaiming this lost sense lies in smell training. However, is there room for improving its efficacy?
Smell training is a therapy recommended by experts for reviving a lost sense of smell. It involves daily exposure to a variety of odors, typically essential oils, herbs, or spices. Much like physiotherapy aids in regaining movement and function after an injury, repeated exposure to odors facilitates the recovery of the sense of smell following an infection or an underlying cause, such as a traumatic head injury.
While laboratory studies have demonstrated the effectiveness of smell training, real-world outcomes have proven less impressive. This is largely due to the lengthy nature of smell training. It may take months before patients notice any improvement, and some may not experience any benefit at all. Research indicates that participation in smell training drops to 88% after three months and further declines to 56% after six months, with individuals reporting no perceived improvement in their olfactory ability.
In response, researchers are exploring avenues to enhance smell training. One intriguing concept under investigation is the integration of “cross-modal associations” into smell training to enhance odor perception and improve results. Cross-modal associations denote the correlation between sensory cues from different sensory systems. For instance, brightness tends to be associated with loudness, and colors are linked to temperature. Recent findings reveal that a blend of sensory inputs from various senses, not just odors, influences the sense of smell, impacting odor identification, pleasantness, and intensity.
A study involving participants, where they were presented with colors and shapes while completing an odor discrimination test, indicated that corresponding odor-color associations led to improved olfactory performance. Building on this, recent research introduced sound-odor associations in smell training through a guidance video, which resulted in enhanced olfactory function compared to smell training alone.
The promising results reported in these studies offer new insights into olfactory science, signaling potential development of more effective treatment options for smell recovery. However, until these advancements materialize, persistent smell training remains one of the best strategies for individuals with a lost sense of smell. Patients are encouraged to stay committed to it in pursuit of regaining this essential sensory perception.
The journey to restore the sense of smell continues to unfold, propelled by innovative research and the relentless dedication to improving the lives of those affected by anosmia.
By Emily Spencer, PhD Candidate in Olfaction, Edinburgh Napier University
