The question of whether a COVID-19 infection affects the senses is frequently raised, and the answer is that the virus often impacts the systems responsible for taste and smell. These sensory disturbances are a distinct feature of infection with SARS-CoV-2, widely reported since the early stages of the pandemic. The resulting sensory changes can vary significantly, ranging from a complete inability to perceive odors and flavors to severe distortions that fundamentally alter the experience of eating and drinking.
Initial Symptoms: Complete Loss of Taste and Smell
The initial phase of sensory disruption commonly involves a sudden and profound absence of sensation. This complete loss of smell, known as anosmia, affects a significant percentage of people with COVID-19, often appearing before or alongside other general symptoms of the illness. The ability to distinguish the five basic tastes—sweet, sour, salty, bitter, and umami—may also be diminished or lost entirely, a condition termed ageusia.
While ageusia is technically the loss of true taste, the overwhelming majority of flavor perception is derived from the sense of smell. When anosmia occurs, the brain is deprived of the complex odor information, leaving only the basic taste sensations. Basic taste sensations like saltiness or sweetness may remain, but the overall enjoyment of food is severely compromised because the rich, layered experience of flavor is missing. This sensory absence is a hallmark of the acute infection phase, and it differs notably from the nasal congestion experienced with a common cold, as the nose often remains physically clear.
The Distorted Reality: Defining Parosmia and Dysgeusia
For many, the sensory experience evolves from a state of complete absence into a “bad taste” as the body begins the recovery process. This unpleasant sensory shift is characterized by two distinct types of distortion: parosmia and dysgeusia. Parosmia is a qualitative distortion of smell, where familiar and pleasant odors are perceived as foul, noxious, or chemical. This symptom often manifests weeks or months after the initial infection has resolved, during the period when the olfactory system is attempting to regenerate.
People with parosmia frequently report that once-appealing aromas like coffee, roasted meat, onions, garlic, or even perfumes suddenly smell like garbage, burnt rubber, or sewage. This distortion transforms the daily experience of food and environment into something highly unpleasant, often leading to food aversion and weight loss. Dysgeusia, the corresponding distortion of taste, causes a persistent, unpleasant, or altered taste in the mouth, often described as metallic, rancid, or excessively bitter. This distorted perception of taste can further complicate eating, as foods may retain a strange aftertaste or simply present with an unappetizing flavor profile.
Why Sensory Changes Occur: The Viral Mechanism
This sensory disruption occurs because the SARS-CoV-2 virus interacts with specific cells located high up in the nasal cavity within the olfactory epithelium. Research indicates that the virus does not infect the olfactory sensory neurons, which are the nerve cells that detect and transmit odor signals to the brain. Instead, the virus targets the surrounding sustentacular cells, which are the support cells responsible for maintaining the environment and health of the neurons.
These supporting cells possess the ACE2 receptor protein, which the virus uses to gain entry and replicate. Once the sustentacular cells are damaged or inflamed, they can no longer properly support the function of the adjacent sensory neurons, leading to the initial loss of smell. The inflammation caused by the immune response also contributes to the temporary dysfunction of the entire olfactory signaling pathway.
Parosmia is thought to result from the imperfect regeneration of the damaged olfactory nerve endings as the epithelium attempts to heal. The re-growing neurons may connect improperly, resulting in the brain misinterpreting a familiar odor molecule as a noxious or distorted smell.
Timeline and Techniques for Recovery
The time required for recovery of the senses can vary widely among individuals; many people regain their sense of smell within weeks or a few months of the initial infection. However, for a subset of the population, these symptoms can persist for many months, becoming a longer-term condition. Studies show that while a large majority of those affected see improvement within two months, a significant number experience prolonged dysfunction.
For those with persistent or distorted sensations, the primary recommended non-invasive management technique is olfactory training, often called smell training. This technique involves deliberately sniffing a set of four distinct, strong odors twice daily over a sustained period of time. The goal of this consistent practice is to encourage the regeneration and reorganization of the olfactory nerves, helping them to correctly identify and signal the scents to the brain. The four common scent categories used are:
- A floral scent like rose.
- A fruity scent such as lemon or citrus.
- A resinous scent like eucalyptus.
- A spicy scent such as clove or cinnamon.