The sudden inability to smell or taste was one of the most distinctive and widespread symptoms of infection with the SARS-CoV-2 virus. Anosmia (complete or partial loss of smell) and ageusia (loss of taste) became highly recognizable indicators of the illness worldwide. This sensory deficit strips away the enjoyment of food and removes the ability to detect hazards like smoke or spoiled food. Because these symptoms affected a significant portion of infected people, the primary question quickly became when, or if, these senses would return.
The Timeline for Sensory Recovery
The majority of individuals who experience a loss of smell or taste during the acute phase of the illness can expect a relatively quick resolution of their symptoms. For a large percentage of patients, the senses begin to return within the first two to four weeks following the initial infection. For many, the median time to regaining these functions can be as short as seven days from the onset of symptoms. Most research indicates that approximately 90% of people with new-onset anosmia or ageusia see their senses return to normal or near-normal function within the first month.
A smaller but significant subset of patients faces a much longer path to recovery, where sensory loss can persist for many months, entering the category of post-COVID-19 conditions. Studies tracking long-term outcomes show that for a small percentage, the loss may last for six months or even a year or more. Even in these protracted cases, the outlook remains generally positive, as recovery is still possible over this extended period. The persistence of these symptoms is usually a result of more extensive damage or slower regeneration within the olfactory system.
The speed of recovery can vary depending on the initial severity of the sensory loss. Younger individuals and those with milder overall COVID-19 symptoms often report a quicker return of their senses. For those whose symptoms linger past the six-month mark, medical consultation is often recommended to explore targeted interventions.
Understanding the Underlying Cause
The sensory loss is not caused by direct infection of the olfactory neurons, the nerve cells responsible for detecting odor molecules. Instead, the SARS-CoV-2 virus primarily targets and infects surrounding support cells within the nasal cavity, specifically the sustentacular cells, which are rich in the ACE2 receptor. When the virus attacks these support cells, it causes inflammation and damage, indirectly impairing the function of the olfactory neurons they support. This disruption leads to the sudden loss of smell.
Because the olfactory neurons themselves are largely spared from direct viral assault, they are often able to recover their function once the inflammation subsides and the supporting cells are repaired. This indirect mechanism explains why the loss of smell is frequently temporary and resolves quickly as the body clears the virus. In cases of prolonged sensory loss, the inflammatory response may be more intense or the process of repairing the supporting tissue is significantly slower.
Navigating Distorted Sensations
As the olfactory system attempts to repair itself, some individuals may experience parosmia, a frustrating intermediate stage characterized by a distorted sense of smell. Parosmia occurs when familiar odors are perceived as foul, metallic, or chemical, often making previously pleasant smells repulsive. This distortion commonly manifests weeks or months after the initial infection, as damaged nerves begin to regenerate and reconnect incorrectly.
Another related condition is phantosmia, where a person perceives a phantom smell that is not actually present. These phantom odors are usually unpleasant, such as the smell of smoke or decay. Both parosmia and phantosmia are thought to be signs that the olfactory nerves are actively regenerating, but the signals being sent to the brain are scrambled.
Managing these distorted sensations often involves identifying and avoiding the specific odor triggers that cause distress. Many people find that common foods, such as onions, garlic, eggs, and roasted meats, become instant triggers. Eating foods that are cold or at room temperature can also help, as they release fewer volatile odor molecules than hot foods.
Strategies to Encourage Sensory Recovery
For those experiencing persistent or distorted sensory function, olfactory retraining, commonly known as smell training, is the most recommended at-home strategy to encourage recovery. This non-invasive technique aims to stimulate the olfactory nerves and rebuild the brain’s ability to recognize and process smells. The method involves repeatedly sniffing a set of four distinct, strong scents from different categories:
- Floral (e.g., rose)
- Fruity (e.g., lemon)
- Spicy (e.g., clove)
- Resinous (e.g., eucalyptus essential oils)
The training should be performed consistently, twice a day, for a duration of at least three to six months. During each session, the person should mindfully sniff each of the four scents for about 20 seconds while actively concentrating and recalling the memory of what the object should smell like. Consistency is a major factor in the success of this therapy, acting like physical therapy for the nose.
Smell training works by encouraging the regeneration and correct re-wiring of the olfactory sensory neurons, improving the brain’s capacity to interpret incoming signals. If the sense of smell has not improved after six months despite consistent training, consulting with an ear, nose, and throat specialist is recommended.