The loss of smell, known as anosmia, or a reduced sense of smell, hyposmia, became a widely recognized symptom of COVID-19. Unlike smell loss from a common cold or flu, which is often due to congestion, COVID-19’s impact typically isn’t accompanied by a stuffy nose. Instead, the virus primarily affects supporting cells in the nasal cavity crucial for smell.
Typical Smell Recovery Timeline
The timeline for regaining one’s sense of smell after a COVID-19 infection varies considerably. Many people recover relatively quickly, often within a few weeks. Approximately 50% regain their sense of smell within two to three weeks, with an additional 40% recovering within eight weeks.
Recovery can be a more gradual process for some, extending over several months. Studies indicate that around 74.1% of patients self-report recovery within 30 days, increasing to 95.7% by 180 days.
Even with high recovery rates, some individuals experience persistent smell issues. About 25% of individuals who lost their sense of smell had not fully regained it within 60 days.
Longer-term studies suggest about 65% of people with COVID-19-induced smell changes regain their senses by 18 months, with 80% to 90% seeing improvement within two years. However, some individuals experience only partial recovery (around 24%) or no recovery at all (approximately 3%).
Factors Affecting Smell Recovery
Several factors can influence the duration and completeness of smell recovery after a COVID-19 infection. The severity of the initial COVID-19 infection plays a role; while smell loss can occur with milder disease, more severe overall COVID-19 symptoms may reduce the chance of complete recovery.
Age and sex are also factors. Younger individuals and females often experience a higher incidence of post-COVID-19 smell disruption, and women may recover slower than men.
The specific SARS-CoV-2 variant also impacts the likelihood of smell loss. Newer variants, like Omicron, are significantly less likely to cause smell and taste loss than earlier variants such as Alpha and Delta. For example, Omicron’s risk of smell loss was around 17%, compared to 50% for Alpha and 44% for Delta.
The Biology of Smell Loss and Regain
COVID-19 affects the sense of smell through a distinct biological mechanism. The SARS-CoV-2 virus primarily targets supporting cells (sustentacular cells) in the olfactory epithelium. These cells express the ACE2 receptor, which the virus uses to enter. Olfactory sensory neurons, responsible for detecting odors, do not typically express ACE2, so the virus does not directly infect them.
Infection of supporting cells leads to inflammation and disruption, indirectly affecting olfactory sensory neurons. This damage can cause cilia retraction or reduce gene activity for building olfactory receptors.
The olfactory system has a remarkable capacity for regeneration. As supporting cells recover, olfactory sensory neurons can regain function, explaining why many individuals eventually recover their sense of smell.
However, during regeneration, some individuals may experience parosmia, a distortion where familiar odors smell unpleasant (e.g., rotten eggs or sewage). This occurs as damaged nerve pathways begin to work again, sometimes regenerating abnormally.
Addressing Persistent Smell Changes
For individuals experiencing prolonged or distorted smell issues after COVID-19, several strategies can help. Smell training, or olfactory training, is a widely recommended approach. This technique involves regularly sniffing strong, distinct scents, typically essential oils such as:
Rose
Lemon
Eucalyptus
Clove or cinnamon
The process involves smelling each scent for 10-20 seconds, twice daily, while focusing on associated memories. This systematic exposure aims to retrain the brain and olfactory pathways. Consistency is important, as improvements can take weeks to months.
If smell changes persist or significantly impact daily life, consult a healthcare professional, such as an ear, nose, and throat (ENT) specialist. They can assess the loss and rule out other causes.
While no single cure exists for persistent post-COVID-19 smell changes, intranasal steroids may be considered, showing improvements in 10-25% of patients. Lifestyle adjustments, like eating foods cold or at room temperature to reduce strong aromas, can also help manage parosmia. For severe symptoms, neuromodulating medications might be explored, though these are typically reserved for challenging cases due to potential side effects.