New respect for our sense of smell

 Smell loss is a more common symptom of Covid than fever or cough. It is also the most reliable predictor of the disease. Most who lose their sense of smell recover it in a matter of weeks, but some have yet to recover it. Many have experienced new smell sensations and, interestingly, use the same words to describe those sensations: metallic, decayed, chemical, burnt, urine. For others, their sense of smell came back broken. Things don’t smell like they should, and the new smell was usually bad (“poo now smelled better than coffee”). 

Prior to this pandemic, most people didn’t consider our sense of smell to be particularly important or interesting. Now, a wide range of scientists are collecting vast amounts of data on our sense of smell. It turns out that olfaction is related to many diseases: smell loss is an early warning sign of diseases such as Alzheimer’s, Parkinson’s, and schizophrenia. People with depression tend to have decreased olfaction and smaller olfactory bulbs than others. Children with autism have different sniff reaction than those who are neurotypical. A wide spectrum of autoimmune or immune-related diseases are associated with smell loss or irregularity.

Here are some more interesting things about our sense of smell: Humans are much better at sensing odors than we’ve been led to believe. Our 400 smell receptors can detect as many as a trillion smells. Sensory neurons are the only type of neuron directly exposed to the outside world, so they sustain an unusual amount of damage. They’re also a rare part of our nervous system that is able to renew itself. Smell has a nearly direct pathway to the centers for memory and emotion in our brains.

Covid is putting our sense of smell on the map. More and more scientists are thinking of smell not as a  "bonus sense" but a dominant one, elevating it, in the words of one scientist, "from a secondary sense to one of the primary things that influences our life."

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