The COVID-19 pandemic frequently caused post-viral anosmia (complete loss of smell) or hyposmia (reduced sense of smell), initially affecting up to half of all patients. The primary cause is damage to the neighboring supporting cells, called sustentacular cells, within the nasal lining, rather than direct infection of the olfactory neurons. Injury to these supporting cells disrupts the function of the olfactory sensory neurons, leading to smell loss. This disruption can also result in a distorted sense of smell, known as parosmia, which often occurs during recovery.
Olfactory Training for Smell Recovery
The most widely recommended, non-invasive method for encouraging smell recovery is olfactory training. This process relies on the principle of neuroplasticity, which is the brain’s ability to reorganize and form new neural connections. Repeated, conscious exposure to distinct odors stimulates damaged olfactory pathways and encourages the regeneration of sensory neurons and their connections to the brain.
The standard protocol involves using four distinct scent categories: floral, fruity, resinous, and spicy. These are typically represented by essential oils such as rose, citrus, eucalyptus, and clove. The training must be performed consistently, sniffing each of the four scents for about 10 to 20 seconds. This process should be repeated twice daily for a minimum of three to six months.
To maximize the therapeutic effect, individuals should actively concentrate on the scent and try to recall the smell from memory while sniffing. Some studies suggest rotating to a second set of four different scents after 12 weeks to provide broader sensory stimulation. Olfactory training is considered the primary and most effective first-line strategy for patients experiencing long-term smell dysfunction after a viral infection.
Clinical Treatments and Potential Supplements
While olfactory training remains the most established self-management strategy, specialists may consider medical interventions. The role of corticosteroid nasal sprays or rinses in the chronic phase of post-viral smell loss is often debated. These topical steroids, like mometasone, are sometimes prescribed to reduce any lingering inflammation, but their benefit over olfactory training alone for long-term recovery is not consistently proven.
Current research is exploring several other treatments that show promise, though they are not yet standard practice. High-dose Vitamin A (retinoic acid) nasal drops have been studied, based on its role in nerve cell health, but more research is needed to confirm its efficacy and ideal dosage. Another emerging therapy is Platelet-Rich Plasma (PRP) injections, where concentrated platelets are injected into the olfactory area to promote tissue healing and regeneration.
Both high-dose Vitamin A and PRP injections are still considered experimental, and patients should approach them with caution under the guidance of a specialist. For chronic post-COVID-19 smell loss, evidence suggests that olfactory training is the most reliable intervention, with pharmacological treatments offering limited or controversial additional benefit.
Navigating Parosmia and Phantom Smells
As the olfactory system repairs itself, a person may experience parosmia, a distortion where familiar odors are perceived as foul or repulsive. These distorted scents are often described as metallic, rotten, or like sewage, triggered by items like coffee, onions, and roasted meats. This differs from phantosmia, which is the perception of a smell when no odor source is present, such as constantly smelling smoke.
While distressing, parosmia indicates that regenerating olfactory nerves are beginning to reconnect, signaling an active recovery process. To cope with the impact on diet and quality of life, patients can employ several practical management strategies:
- Identify and strictly avoid specific trigger foods that cause the most offensive distortion.
- Consume foods at cooler temperatures, as heat releases more volatile odor molecules that intensify the parosmic effect.
- Eat simple, bland meals.
- Use a nose clip temporarily while eating to manage sensory overload during challenging phases.
Understanding the Recovery Timeline
For most people who experience smell loss after COVID-19, recovery begins relatively quickly, often within the first few weeks. However, for those with persistent issues, improvement typically occurs gradually over a much longer period. While substantial recovery is often seen within the first few months, improvement can continue for up to two years post-infection due to the olfactory neurons’ capacity for regeneration.
Persistent anosmia is generally considered chronic if it lasts beyond six to twelve months. If there is no improvement after several months of symptoms, or if the loss is severe, it is advisable to consult a specialist. Seeking professional evaluation ensures that other potential causes for the smell loss are ruled out and that a structured rehabilitation plan can be developed.