Parosmia is a condition that alters how individuals perceive familiar scents, transforming them into distorted and often unpleasant odors. Unlike anosmia, which involves a complete loss of smell, or phantosmia, where a person smells something that is not present, parosmia means an existing smell is perceived incorrectly. This qualitative distortion can make once-pleasant aromas, such as coffee or a favorite food, smell foul or repulsive.
Primary Underlying Causes
Parosmia often emerges following specific events or conditions that affect the olfactory system. Viral infections, particularly respiratory viruses, are a common precursor. The SARS-CoV-2 virus, responsible for COVID-19, has been widely associated with a surge in parosmia cases, often appearing during the recovery phase after an initial loss of smell. The virus and the inflammation it causes can damage the delicate olfactory neurons.
Physical injury to the head can also initiate parosmia. Head trauma, including concussions, can disrupt the olfactory system, particularly affecting the frontal lobe and the olfactory bulbs. The onset of parosmia in these cases may not be immediate, sometimes appearing weeks or even months after the initial injury.
Other upper respiratory infections, such as the common cold or influenza, can similarly lead to parosmia. These infections can cause damage to the olfactory neurons, leading to distorted smell perception. Exposure to certain toxins or chemicals, including pollution, has also been linked to parosmia by damaging the olfactory receptor neurons. Additionally, some nasal conditions like polyps or complications from sinus surgery can affect the olfactory pathway, potentially contributing to parosmia.
The Olfactory Pathway Connection
Distorted smells result from specific biological and neurological processes within the olfactory pathway. The primary causes often damage the olfactory sensory neurons located in the nose. These specialized cells detect odors and transmit signals to the brain. When injured, these neurons can regenerate.
During this regeneration process, the new neurons may “miswire” to the brain’s olfactory bulb. This miswiring results in scrambled or altered signals being sent to the brain, which then struggles to interpret the familiar smell correctly. The olfactory bulb plays a crucial role in processing these smell signals.
Damage or inflammation within the olfactory bulb can further contribute to the altered processing of olfactory information. While the initial damage often occurs in the peripheral olfactory system (the nose), the brain’s processing also plays a role in the perception of distortion. Central nervous system involvement, including changes in brain regions, can influence how these misfired signals are ultimately experienced.
Common Olfactory Triggers
Understanding the specific smells that commonly trigger parosmia provides insight into the daily experience of individuals with this condition. Many people report that certain food and drink categories become particularly problematic. Common culprits include coffee, onions, garlic, and cooked meats. Other frequently cited triggers include eggs, chocolate, toothpaste, bell peppers, cucumbers, and citrus fruits. Beyond food, everyday items like certain cleaning products and perfumes can also elicit a distorted response.
The distortion is often described as unpleasant and repulsive. Individuals often perceive these once-normal smells as metallic, rotten, chemical, burnt, or fecal. Some describe the sensation as “nauseating” or like “burnt rubber.” This change in smell perception impacts daily life.
The distorted smells can lead to food aversion, making eating a challenge and resulting in weight loss. The condition can also affect the perception of one’s own body odor, which some individuals describe as foul, regardless of hygiene. Such sensory experiences can affect quality of life, social interactions, and emotional well-being.