Losing the sense of smell to COVID-19 is so common it's even skewing product reviews. Fortunately, although this can be long-term, it's seldom permanent. One team of researchers have been comparing techniques to bring the fifth (or is it fourth) sense back, and found “smell training” a better option than steroids.
"The huge rise in smell loss caused by Covid-19 has created an unprecedented worldwide demand for treatment, said Professor Carl Philpott of the University of East Anglia in a statement. The human sense of smell is much weaker than most other animals (something some scientists attribute to us outsourcing it to dogs), but it still important to us, both for pleasure and to warn of dangers like smoke. It's no surprise people who have lost it are very keen to get it back.
"Around one in five people who experience smell loss as a result of Covid-19 report that their sense of smell has not returned to normal eight weeks after falling ill,” Phillpott continued.
Many doctors have turned to corticosteroids to help. Used to lower inflammation, including for asthma sufferers' respiratory tract, word got around they might be the solution. Despite established side-effects such as high blood pressure and mood-swings, corticosteroids have been considered safe enough to be widely prescribed.
That doesn't mean they work, against a new condition, however. Phillpott sought out studies on corticosteroid effectiveness for smell restoration. In International Forum of Allergy and Rhinology, he and co-authors conclude; “Evidence supporting their usefulness is weak.” This is largely based on studies of related olfactory dysfunction in humans and animals, since the Covid-19 testing hasn't been done.
Fortunately, there is an alternative. Philppott recommends sniffing four different strong scents at least twice a day over several months, known as smell training “It has emerged as a cheap, simple and side-effect free treatment option for various causes of smell loss, including Covid-19,” Phillpott said.
There has not been time to truly explore how smell training works, but Phillpott attributes its success to “neuroplasticity”, the capacity of the brain to repurpose neurons to replace those that have been damaged. The authors think smell loss; “Likely results from two separate pathological processes. First, an obstructive inflammatory process blocking odorant access at an early stage of the disease; and second, a neurosensory post-infectious smell loss .”
The inflammation should come right of its own accord; smell training can deal with the neurosensory issues.
Given that smell returns of its own accord in at least 90 percent of cases, and this can be hastened with smell training, Philpott and co-authors consider the risks of corticosteroids to outweigh the benefits in most cases. There could be exceptions, however, where the cause might be something this class of drugs does work against, such as chronic sinusitis. In those cases, nasal sprays might be the best way to take the drugs, the authors suggest.