The COVID-19 pandemic brought widespread attention to the loss or distortion of the sense of smell. This condition, medically termed anosmia (complete loss) and parosmia (distorted smell), became a frequently reported indicator of infection with the SARS-CoV-2 virus. Studies indicate that almost half of individuals with COVID-19 experienced some change in their sense of smell or taste, impacting their enjoyment of food and their ability to detect environmental cues.
Common Recovery Timelines
For many individuals who experience a loss of smell due to COVID-19, this sense gradually returns over a period of weeks to a few months. Research indicates that a majority, around 88% of patients, recovered their sense of smell within two months, with a median recovery time of approximately 11.5 days. Similarly, some studies suggest that four out of five COVID-19 survivors who lost these senses regained them within six months. While most people experience improvement relatively quickly, a subset may face a more prolonged recovery.
The duration of smell impairment can vary considerably among individuals. Approximately 23% of patients reported a loss of smell lasting longer than a month. Persistent anosmia was observed in about 18.8% of patients after a follow-up period of 67 days. For those experiencing parosmia, a distorted sense of smell, symptoms have been reported to last up to 16 months in some instances. A notable study also found that around 24% of COVID-19 survivors continued to experience parosmia 2.6 years after their initial diagnosis.
Several factors can influence the speed and completeness of smell recovery. Younger individuals, particularly those under 40, tend to recover their sense of smell at a higher rate compared to older adults. Additionally, some findings suggest that women may experience a slower recovery of their sense of smell and taste than men. The initial severity of the smell dysfunction can also play a role in the recovery prognosis.
The presence of other symptoms during the acute phase of illness might also be associated with recovery outcomes. Individuals who experienced nasal congestion during their COVID-19 infection had a higher likelihood of smell recovery. Conversely, those with a history of shortness of breath during COVID-19 were less likely to fully regain their sense of smell.
How COVID Impacts Smell
The mechanism by which COVID-19 causes smell loss involves specific cells within the nasal cavity, rather than directly attacking the nerve cells responsible for detecting odors. The SARS-CoV-2 virus primarily infects supporting cells, known as sustentacular cells, located in the olfactory epithelium. These supporting cells possess the ACE2 receptor protein, which the virus uses to enter human cells.
When these sustentacular cells are infected, it leads to inflammation and disruption in the nasal lining, which indirectly affects the function of the adjacent olfactory neurons. The temporary impairment of these supporting cells, rather than direct damage to the neurons themselves, helps explain why smell loss can occur rapidly and why many individuals eventually recover their sense of smell. The body’s immune response to the virus, including the release of inflammatory proteins called cytokines, can also contribute to the duration of this dysfunction by altering genetic activity in olfactory nerve cells.
The impact of COVID-19 on smell can manifest in different ways. As individuals begin to recover, they might experience parosmia, which is a distortion of smells, causing familiar odors to smell unpleasant, such as like rotting or burning substances. The prevalence of parosmia has been observed to increase over time in some studies, affecting a significant percentage of individuals during their recovery phase.
Supporting Your Sense of Smell
For individuals experiencing persistent or distorted smell loss after COVID-19, specific interventions can help support the recovery process. Olfactory training, also known as smell training, is a widely recommended non-pharmacological approach that involves repeatedly sniffing a set of distinct odors. This training typically includes four primary scents, such as rose, lemon, clove, and eucalyptus, which are sniffed twice daily for 20 to 30 seconds each. Consistent practice for at least four months, and sometimes up to a year, is often suggested for optimal results.
The rationale behind smell training is that it helps to activate the olfactory nerves, strengthen the connections between the nose and the brain, and encourage the brain to refocus on and interpret odors. While most studies indicate a positive impact of olfactory training on improving smell function, some research suggests it may not be superior to placebo alone, though it remains a widely recommended practice.
It is advisable to consult a healthcare professional if smell loss persists beyond an initial recovery period, generally after a few weeks to a month. If there is no noticeable improvement after approximately two months, seeking an evaluation from an ear, nose, and throat (ENT) specialist is recommended. Early assessment can help identify any other underlying issues and determine appropriate next steps for care.
Coping with a diminished or altered sense of smell can be challenging, impacting aspects of daily life beyond just enjoying food. Individuals often find it helpful to focus on other sensory qualities of food, such as texture, temperature, and visual appeal, and to incorporate various spices to enhance the eating experience. Awareness of safety concerns, such as the inability to detect gas leaks, smoke, or spoiled food, becomes important when the sense of smell is compromised. Recognizing the potential for emotional impacts, including feelings of frustration or anxiety, and seeking support if needed, can also be beneficial.