Phantosmia, the sensation of perceiving odors that are not present, emerged as a distinct and often distressing long-term symptom following infection with SARS-CoV-2. While the initial loss of smell, known as anosmia, was a common early indicator, phantosmia represents a distortion of the olfactory system that can develop weeks or even months into recovery. This phantom smell is not a sign of residual virus, but rather a manifestation of lingering damage to the machinery responsible for processing scent signals. Understanding the biological trigger and the expected recovery timeline is important for navigating this challenging sensory experience.
Defining Phantosmia and Common Sensations
Phantosmia is defined as an olfactory hallucination, meaning the perception of a smell without an external odor source to trigger it. This condition is one of several qualitative olfactory dysfunctions that occur as the sense of smell attempts to regenerate following viral damage. Unlike a simple loss of smell, phantosmia involves the brain creating a scent based on faulty signals from the nasal cavity.
The smells experienced are overwhelmingly described as unpleasant, a condition sometimes called cacosmia. People frequently report smelling things like burning rubber, smoke, garbage, chemicals, burnt toast, rotting food, or a metallic or sickly sweet scent. These phantom smells can be constant or come and go, and they significantly impact daily life by making food consumption and basic self-care difficult.
How COVID-19 Triggers Olfactory Dysfunction
The SARS-CoV-2 virus does not primarily infect the olfactory sensory neurons (OSNs). Instead, the virus targets the supporting cells, known as sustentacular cells, within the nasal cavity’s olfactory epithelium. These sustentacular cells are equipped with the ACE-2 receptors and the proteases the virus uses for entry.
Infection of these supporting cells triggers a robust inflammatory response characterized by the infiltration of immune cells and the release of pro-inflammatory cytokines. This inflammation causes damage to the neighboring OSNs, including the physical loss of their odor-detecting cilia. The subsequent damage disrupts the normal signaling pathway, which is believed to lead to the misfiring of partially recovered neurons. This disorganized electrical signaling to the brain is the likely source of the phantom or distorted smell sensations associated with phantosmia.
Expected Duration and Recovery Timeline
The duration of post-COVID phantosmia varies, but recovery is generally characterized as a slow, gradual process. While some people experience improvement within a few weeks, the condition can often persist for many months. Studies have indicated that symptoms can last beyond six months for many affected individuals, with a small fraction experiencing long-term dysfunction lasting a year or more.
Phantosmia is often observed as the olfactory system begins to regenerate, sometimes appearing as a late-onset symptom months after the initial infection has resolved. The recovery timeline is dependent on factors such as the extent of the initial nerve damage and the body’s regenerative capacity. The gradual return of the sense of smell reflects the ongoing process of nerve repair and re-establishment of neural connections to the brain.
Practical Management Strategies
Smell training, also known as olfactory retraining, is the primary non-invasive intervention recommended for managing post-viral olfactory dysfunction. This technique functions like physical therapy for the olfactory system, aiming to stimulate nerve regeneration and reorganize the brain’s processing of scents. Training involves the systematic sniffing of four distinct essential oils twice daily for several months.
The four scents typically used represent four different odor categories:
- Rose
- Lemon
- Eucalyptus
- Clove
When performing the training, a person should inhale each scent for about 10 to 15 seconds while actively concentrating and recalling the memory of the true smell. Consistency over a period of 12 to 24 weeks is necessary before a notable improvement may be observed. Some healthcare providers may suggest the use of intranasal steroids to reduce inflammation within the nasal lining. Consulting an ear, nose, and throat (ENT) specialist is advisable if symptoms persist beyond a few months to rule out other possible causes and discuss further interventions.