COVID-related loss of taste and smell reversible over time, finds study

Great news for those who lost some or all of their sense of smell or taste due to COVID-19: The effect, while persistent, does not appear to be permanent. A study led by the University of Trieste, Italy, has found that despite the loss of taste and smell associated with COVID-19, progressive recovery and restoration of the senses occurs slowly over time.

In a research letter, "Olfactory and Gustatory Function 3 Years After Mild COVID-19—A Cohort Psychophysical Study," published in JAMA Otolaryngology–Head & Neck Surgery, the team investigated the long-term loss of the ability to smell and taste in 88 individuals who had mild symptoms of COVID-19 who had tested positive for SARS-CoV-2 in March and April of 2020.

Psychophysical evaluations were conducted 1, 2, and 3 years after SARS-CoV-2 infection using the Sino-nasal Outcome Test 22 (SNOT-22), extended Sniffin' Sticks test battery, and Taste Strips test.

In self-reported assessments using SNOT-22, smell or taste dysfunction decreased over 3 years. Starting at a high of 64.8% during the acute phase, dysfunction fell to 31.8%, 20.5%, and 15.9% at 1-year, 2-year, and 3-year follow-ups, respectively.

The extended Sniffin' Sticks test battery saw dysfunction decline to 40.9%, 27.3%, and 13.6% at 1-, 2-, and 3-year evaluations, respectively. Taste Strips testing was 26.1%, 13.6%, and 11.4% at 1-, 2-, and 3-year evaluations, respectively.

The study suggests a favorable rehabilitation of smell and taste function over the 3-year observation period, with taste showing lower frequency and faster recovery than smell.

The loss of the ability to taste and smell was such a common effect of the initial variety of SARS-CoV-2 that the symptom was considered an early diagnostic indicator before testing was widely available.

Aside from the decline in the ability to enjoy favorite foods, a loss of smell could also be dangerous. Natural gas is artificially scented so people can smell a leak before an accident occurs. The smell of smoke can provide an alert of a fire before the sight of smoke is noticeable.

It is estimated that most infected people had sensory loss during the early waves of the pandemic, which is consistent with the current finding. Subsequent variants have far less impact on taste and smell, with the omicron variant having almost no perceptible impact.

For those who lost these senses, there was uncertainty about when or even if the normal function would return. One of the many difficulties in dealing with a novel infection like COVID-19 is that there is no clinical history to refer to and no past record of recovery time upon which to rely. Thankfully, the current study finds that the effects are not permanent, and recovery is slowly taking place.

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