The loss of smell, known as anosmia, and the reduced sense of smell, or hyposmia, were quickly recognized as distinct and common symptoms of COVID-19 infection. Unlike a typical cold, this sudden inability to detect odors often occurs without a blocked nose. The virus does not primarily attack the sensory neurons responsible for detecting smells, but instead targets the supporting cells in the olfactory epithelium. This localized inflammation and damage disrupts the neural pathway, leading to the temporary or complete loss of function.
The Typical Timeline for Smell Recovery
For most individuals who lose their smell due to COVID-19, recovery is relatively short and occurs spontaneously within the first few weeks. Many studies indicate that the sense of smell begins to return within two to four weeks following the onset of symptoms. One study suggested that the average duration of olfactory dysfunction for mild COVID-19 cases was approximately 21.6 days.
This rapid return of function is the most common outcome. Within the first month, a large percentage of affected individuals report a complete or near-complete resolution of their smell loss. The recovery speed can be influenced by several factors, including the severity of the initial COVID-19 illness, a patient’s age, and any pre-existing nasal or sinus conditions.
While the most significant recovery often occurs early, the process continues over a longer period for some people. Approximately 95% of patients who experience this symptom regain their sense of smell by six months post-infection. Studies observing patients for up to two years have shown that recovery can continue gradually.
Defining Persistent Loss and Distorted Smell
When anosmia or hyposmia extends past four weeks, it is classified as prolonged, and symptoms lasting beyond six months are considered persistent. This persistent loss suggests that the damage to the olfactory system requires a longer period for the supporting cells and neurons to regenerate and repair the neural connections.
Beyond the quantitative loss of smell, many patients experience qualitative changes, which are distinct and often more distressing. Parosmia is the medical term for a distorted sense of smell, where familiar odors, such as coffee or perfume, are perceived as highly unpleasant, often smelling rancid, chemical, or like rotten eggs. This distortion typically arises during the recovery phase, weeks or months after the initial infection, as the regenerating olfactory nerves reconnect incorrectly.
Another qualitative change is phantosmia, which involves smelling odors that are not actually present in the environment, akin to an olfactory hallucination. Both parosmia and phantosmia indicate that the olfactory system is actively attempting to rewire itself, though incorrectly at first. If smell dysfunction continues past four weeks, or if qualitative changes begin to occur, consultation with a healthcare provider is recommended to assess the condition.
Practical Strategies for Olfactory Rehabilitation
For those experiencing prolonged smell loss, the primary and most accessible intervention is olfactory rehabilitation, commonly known as smell training. This process acts like physical therapy for the olfactory nerve, aiming to stimulate nerve regeneration and retrain the brain to correctly identify odors. Consistency is a determining factor for the effectiveness of this technique, which requires dedicated daily effort over an extended period.
The standard protocol involves using four distinct scent categories, often represented by essential oils:
- Floral
- Fruity
- Spicy
- Resinous
The patient is instructed to sniff each scent for about 15 to 20 seconds, focusing intently on the memory of the smell, and repeating the process twice daily. This training should be maintained for at least three months, with specialists suggesting a six-month commitment or longer, often alternating the four scents every few months to introduce new stimuli.
In addition to smell training, medical interventions may be considered depending on the patient’s specific circumstances. A doctor might recommend a course of nasal steroid sprays, such as fluticasone, which can help reduce any residual inflammation in the nasal passages that may be hindering recovery. Some practitioners also suggest incorporating supplements like Omega-3 fatty acids, based on the theory that they can support the healing and regeneration of the olfactory nerves.