Parosmia Explained: Why Smells Change After COVID and What You Can Do

What is parosmia?

Parosmia is a condition where your sense of smell is distorted. Instead of losing the ability to smell entirely, you smell things, but they smell wrong. Coffee might smell like burnt rubber. Garlic might smell like sewage. Toothpaste, shampoo, cooking food, or your own body can all trigger an unpleasant or unrecognizable odor that doesn't match what you know those things should smell like.

It is different from anosmia, which is a complete absence of smell, and different from hyposmia, which is a reduced but still somewhat functional sense of smell. Parosmia is specifically about distortion. The signals are getting through, but they're scrambled.

For many people experiencing it, parosmia is deeply distressing. It can affect appetite, mental health, social interactions, and quality of life. Foods that were once enjoyable can become nauseating. The unpredictability of which smells will be affected adds to the frustration.

What causes parosmia?

Parosmia is most commonly associated with post-infectious olfactory dysfunction, smell disruption that follows a viral illness. While it has been documented in the medical literature for decades following various upper respiratory infections, it received significantly more attention after the COVID-19 pandemic, when large numbers of people began reporting distorted smell during or after recovery.

The mechanism is not fully understood, but researchers have proposed several explanations. One widely discussed theory is that parosmia reflects a stage in olfactory neuron recovery. When olfactory receptor neurons are damaged by a virus, the body can regenerate them. The olfactory epithelium is one of the few areas in the nervous system capable of ongoing neuronal regeneration. However, newly regenerated neurons may not immediately form correct connections to the olfactory bulb. During this period of partial or disordered reconnection, incoming scent signals may be misinterpreted by the brain.

Under this framework, parosmia is not necessarily a sign that things are getting worse. Some researchers have suggested it may indicate that recovery is underway, but incomplete. A 2020 study by Reden et al. found that the presence of parosmia was associated with better olfactory outcomes over time compared to patients without parosmia, though individual experiences vary and this finding does not apply to every person.

How common is parosmia after COVID?

Estimates vary across studies. A systematic review of post-COVID olfactory dysfunction found that parosmia was reported by a meaningful portion of patients who initially experienced smell loss. Some studies have reported rates as high as 40-60% among those with persistent post-COVID olfactory symptoms, though the numbers depend heavily on how parosmia is defined and measured in each study, and when after infection the assessment takes place.

What the research says about olfactory training and parosmia

Several published olfactory training studies have included participants with parosmia. The classical Hummel four-scent protocol (sniffing four distinct odor categories twice daily for at least 12 weeks) was not originally designed specifically for parosmia, but researchers have examined its use in this population.

Altundag et al. (2022) specifically studied a modified olfactory training protocol in post-COVID patients with parosmia. The modified approach involved rotating the training scents at regular intervals rather than using the same four scents throughout the entire training period. This study contributed to a growing body of research exploring whether protocol modifications might be relevant for parosmia specifically.

It is important to note that the evidence base for olfactory training in parosmia specifically is smaller than the evidence base for anosmia and hyposmia. The area is one of active research, with several ongoing studies examining different approaches.

The D'Ascanio et al. (2022) randomized controlled trial compared olfactory training to intranasal budesonide in post-COVID patients and included participants with various types of olfactory dysfunction, including parosmia. Combination approaches (using olfactory training alongside other interventions) are an area of current investigation.

What you can do if you have parosmia

If you are experiencing parosmia, especially following a viral illness, here are some practical considerations:

See a healthcare provider. An ENT specialist (otolaryngologist) can evaluate your olfactory function, rule out other causes, and discuss appropriate approaches for your specific situation. Parosmia can have causes other than viral infection, and a clinical evaluation is the right starting point.

Understand that timelines vary. Published research on post-infectious olfactory dysfunction, including parosmia, describes a range of recovery timelines. Some individuals see improvement within weeks or months. Others experience symptoms for a year or longer. Group-level data from clinical studies does not predict any individual's outcome.

Learn about olfactory training. The published research on olfactory training spans more than 15 years and includes multiple study designs. If you are considering olfactory training, our article What Is Olfactory Training? A Complete Guide provides an overview of the research foundation and the protocol.

Track your experience. Many people with parosmia find it helpful to keep a simple log of which scents are distorted, which are perceived normally, and how things change over time. Gradual shifts can be difficult to notice day-to-day but become apparent over weeks or months.

Be patient with yourself. Parosmia can affect your relationship with food, your social life, and your mental health. These are real impacts. Support communities like AbScent and Fifth Sense connect people who are going through similar experiences.

Parosmia and The Olfactory Training Kit

The Olfactory Training Kit contains four essential oils (lavender, lemon, clove bud, and eucalyptus) representing the four primary odor categories used in the published research. The kit provides a three-month supply at the twice-daily protocol described in the literature.

We do not claim that olfactory training will resolve parosmia for any specific individual. What we can say is that olfactory training is a structured practice with a published research base, that several studies have included participants with parosmia, and that the approach is considered by researchers to be a low-risk behavioral intervention.

If you are experiencing parosmia, we encourage you to discuss your options with a healthcare provider before beginning any new practice.

The content on this page is for informational and educational purposes only. It is not medical advice and does not replace evaluation or advice from a qualified healthcare provider.