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Ask anyone what the symptoms of depression are, and they are likely to ramble off the same list. Sadness. Hopelessness. A loss of enjoyment. Emotional numbness. Isolation. These basics have been drummed into our memory and created an exhaustive picture of how the symptoms of depression manifest.

A symptom we don’t often associate with depression is the loss of smell.

This often-ignored phenomenon has long left researchers puzzling the connection. Why do those with depression have difficulty smelling things? Why can’t they differentiate different odors? Why do so many with depression also suffer from dysosmia and anosmia?

The connection between depression and olfactory function.

When you’re trying to clarify the symptoms of mental illness, the process can be tricky. It’s hard to draw a line of correlation between something like dysosmia and depression because there are so many variables involved. What causes what? What is the chain of connection between them?

You have to start with the basics and the facts.

We know that smell has a direct effect on moods. Those with a healthy sense of smell and taste find more enjoyment in life. When you smell a candle that reminds you of your childhood home, or you pass by someone wearing your dad’s cologne, you are filled with memories, and those memories can trigger your emotions (and mood).

If smell and taste can equate to positive moods, then there could be a reasonable assumption that the opposite is true.

For years, researchers have theorized that olfactory function has a direct effect on happiness (and depression). The greatest speculation points to old age. As we get older, our olfactory abilities decline. We become less able to smell and taste. Researchers have speculated that this could relate to the rise of depression in older age groups.

But is the relationship correlative or causative? That’s the trickier question to answer.

Where is the link? Is there one at all?

Studies have shown that olfactory function may occur because of changes in the brain caused by stress, depression, and excess corticosteroids. The root of that lies in our brains themselves. Olfaction and mood share some of the same brain structures, specifically the entorhinal cortex, hippocampus, amygdala, and orbital-prefrontal cortex.

When we are subjected to long-term stress or fall into a pattern of depression, these structures become changed. Those physical changes come down to neural changes, which affect mood and which may be the root of olfaction dysfunction in those who are depressed. That doesn’t necessarily mean that depression causes olfactory dysfunction. In that instance, they’re more like distantly related cousins.

Inflammation and infection can also create symptoms like dysosmia…and can also be linked to depression. A recent study of COVID-19 patients found that those who experienced a loss of smell had a higher incidence of depression. But does that mean that one causes the other? Or does the experience of COVID itself cause depression?

Third factors (variables) undeniably play a role. Stress, inflammation, and anatomical changes all contribute to depression and olfactory decline. Unfortunately, similarities do not paint a complete picture. Because of the endless number of variables at play, these things may ultimately not be related to one another.

Still, there is compelling evidence out there that depression can affect olfactory function in some patients.

Researchers who subscribe to this theory point to studies that have shown depression to trigger olfactory deficits because of the decline in cognitive ability. Depression changes the way you think and your ability to think. When your cognitive processing is affected. Your brain spends its power doing anything other than pumping energy into your sense of smell.

How could we possibly know this?

Functional imaging studies. By taking scans of depressed patients (clinical) both with and without olfactory systems, researchers observed very little relationship between depression and “olfactory bulb volume.” Therefore, they theorized that the loss of olfactory function in depressed patients would relate more to the brain’s fluctuating cognitive abilities.

Does this new information have the potential help people with depression?

Of course! The connections being examined in these studies offer up a lot of interesting prospects in terms of the treatment and diagnosis of depression. If, indeed, it can be proven that depression equals a loss of smell — practitioners could be empowered to diagnose patients earlier and more accurately.

There’s also the potential for helping practitioners identify the severity of depression more accurately. If a causal link can be determined between depression and loss of smell, it could help indicate that a patient is a more progressed form of the illness and, therefore, in need of more serious intervention.

Treatment, too, could be improved.

If olfactory function affects depression, then some patients could be offered therapies like olfactory training (OT) and olfactory enhancement (OE). In these therapeutic modalities, patients are exposed to different odor concentrations over time. Some early studies have shown positive results when using OT and OE in the treatment of depression.

Giving patients a greater spread of treatment options is a good idea. It allows for more individually tailored care and a holistic approach to getting the mind back on track.

These promising new realizations should come with joy for all those who have suffered from depression through the years. We are learning more and more about ourselves each day, and in that knowing, we are becoming better for ourselves and the world.

Brogan, M.K. (n.d.). 43% of respondents report feeling depressed after losing sense of smell or taste related to COVID-19. [online] VCU News. Available at: https://news.vcu.edu/article/43_of_respondents_report_feeling_depressed_after_losing_sense.

Leon, M. and Woo, C.C. (2022). Olfactory loss is a predisposing factor for depression, while olfactory enrichment is an effective treatment for depression. Frontiers in Neuroscience, 16. doi:https://doi.org/10.3389/fnins.2022.1013363.

Rochet M, El-Hage W, Richa S, Kazour F, Atanasova B. Depression, Olfaction, and Quality of Life: A Mutual Relationship. Brain Sci. 2018 May 4;8(5):80. doi: 10.3390/brainsci8050080. PMID: 29734670; PMCID: PMC5977071.