The loss or alteration of the sense of smell, known as olfactory dysfunction, became one of the most distinctive neurological symptoms of COVID-19 infection. This sensory change is common, causing frustration for many survivors whose ability to detect odors does not immediately return. While the symptom resolves quickly for most, the disruption can linger for months or even years for a notable minority. Understanding the different forms this sensory change takes and the expected timelines provides a clearer picture of what to anticipate following an infection.
Defining Sensory Changes
Sensory changes experienced after a COVID-19 infection manifest in distinct ways, and recognizing the difference between them helps track recovery. Anosmia refers to the complete inability to detect any odors, often reported early in the infection course. A less severe form is Hyposmia, which involves a partial or reduced ability to smell, meaning scents are significantly fainter or harder to recognize.
A particularly disruptive symptom emerging during recovery is Parosmia, a distortion of smell. With parosmia, familiar odors become perceived as unpleasant, rancid, or “wrong,” such as coffee smelling like burnt rubber. This distorted perception signals that damaged olfactory nerves are attempting to regenerate, but the brain incorrectly interprets the signals.
The Typical Recovery Timeline
For the majority of individuals, the sense of smell returns relatively swiftly, often within the first few weeks after the initial infection. Research indicates that the median recovery time for those with rapid resolution is approximately 11.5 days from the onset of symptoms. Substantial recovery is seen in 88% to 90% of patients within the first one to three months.
However, for others, the recovery process is prolonged and may take many months. Studies show that roughly 20% to 33% of people continue to experience some level of smell dysfunction past the two-month mark. By six months post-infection, around 81% of patients report a subjective recovery of function.
Even for those with long-term loss, recovery remains possible. Long-term studies show that about 90% of patients who initially lost their sense of smell fully regained it within two years. Factors associated with a faster recovery include younger age (under 50) and a milder degree of initial smell loss. Women have also been observed to take longer to recover their sense of smell compared to men.
Strategies for Olfactory Recovery
Individuals experiencing persistent smell loss can encourage the regeneration of their olfactory nerves through a structured process called olfactory training. This method is recommended as the first-line treatment, regardless of the severity or duration of the loss. Olfactory training involves deliberately smelling a set of four distinct scent categories twice daily for several months.
Olfactory Training Protocol
The typical protocol uses four essential oils representing different scent groups:
- Flowery (like rose)
- Fruity (like lemon or citrus)
- Spicy (like clove or cinnamon)
- Resinous (like eucalyptus)
Each scent should be sniffed gently for about 10 to 15 seconds. The user should focus on visualizing the object or food associated with the smell. This training acts as physical therapy for the olfactory system, harnessing the unique neuroplasticity of the smell nerve, which has a capacity for regeneration that other cranial nerves lack.
Patients are advised to perform this exercise twice a day for a minimum duration of 12 weeks. Many specialists suggest continuing for up to six months or longer for the best results. While olfactory training is the most proven strategy, emerging research suggests that supplements, such as Omega-3 fatty acids, may offer additional benefit by helping to reduce inflammation and support nerve health.
When to Seek Medical Consultation
While spontaneous recovery is the most common outcome, persistent smell loss should prompt a consultation with a specialist at specific points. If there is no noticeable improvement after approximately three to six months, evaluation by a medical professional is advised. This is particularly true if the loss is severe or if the individual is experiencing highly distressing symptoms like parosmia.
The appropriate specialists to consult are usually an Otolaryngologist (ENT) or a physician at a dedicated smell and taste clinic. These specialists can perform objective assessments of olfactory function to gauge severity and rule out other potential causes of smell loss unrelated to the virus. Although there are currently no globally approved medications specifically to restore smell, specialists may discuss options such as steroid treatments or high-volume saline nasal irrigations, depending on the underlying pathology.