Conditions linked to loss of smell include:
- Alzheimer’s disease
- Anxiety disorder
- Bipolar disorder
- Depression
- Fibromyalgia
- Frontotemporal dementia
- Glioblastoma (brain cancer)
- Heavy metal exposure
- Huntington’s disease
- Long COVID
- Menopause
- Multiple sclerosis
- Obsessive-compulsive disorder (OCD)
- Post-traumatic stress disorder (PTSD)
- Schizophrenia
What Causes Loss of Smell?
With many medical conditions, people may experience a loss of smell before any other symptoms — and inflammation could be to blame.
“The loss of the sense of smell is accompanied by an increased level of chronic inflammation, which has been shown to increase the risk of many medical conditions,” says lead study author Michael Leon, PhD, a professor emeritus of neurobiology and behavior at the University of California in Irvine.
While the exact ways inflammation impacts the brain vary, the loss of smell is a good indication that people should see a doctor to investigate what might be wrong, according to the research review.
“The sense of smell is like the ‘canary in the coal mine,’ with any deficit or disorder signaling that something in your brain has gone awry,” says Zara M. Patel, MD, professor of otolaryngology at Stanford University School of Medicine in California, who wasn’t involved in the research review.
Something “awry” could even be cancer, specifically glioblastoma, a type of brain tumor.
Many factors could contribute to loss of smell, such as sinus infection, air pollution, and smoking. But in some cases a brain issue may be the key reason, says Qu (Teresa) Tian, PhD, an associate scientist at the National Institute on Aging, who wasn’t involved in the research review.
“The connection between loss of smell to mood disorders and neurodegenerative diseases, such as Alzheimer’s disease, may be explained by brain deterioration and pathology,” Dr. Tian says.
The Connection Between Smell and Emotions
With mood disorders like anxiety and depression, loss of smell may be an early symptom because the olfactory system is directly connected to key areas of the brain responsible for the sensation of pleasure and emotions, says Jayant Pinto, MD, a surgery professor and vice dean of faculty affairs at the University of Chicago, who wasn’t involved in the research review.
“This would be one reason decreased smell function is associated with mental health problems like anxiety and depression,” Dr. Pinto says.
Treating Loss of Smell Can Nurture Brain Health
The scientists behind the research review point out that it may be possible to prevent or remedy many neurological, cognitive, and behavior problems associated with a loss of smell with a type of treatment known as olfactory enrichment. This can involve aromatherapy, or exposure to essential oils or specific scents, as a way to stimulate neurotransmitters in the brain, reduce inflammation, and improve memory.
“Olfactory enrichment not only improves the sense of smell, but by simulating that sense, you activate the memory and emotional areas of the brain, keeping them healthy,” Leon says.
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