Parosmia is a term used to describe health conditions that distort your sense of smell. If you have parosmia, you may experience a loss of scent intensity, meaning you can’t detect the full range of the scents around you.

Sometimes parosmia causes things you encounter every day to seem like they have a strong, disagreeable odor.

Parosmia is sometimes confused with another condition called phantosmia, which causes you to detect a “phantom” scent when there’s no scent present.

Parosmia is different because people who have it can detect an odor that’s present — but the scent smells “wrong” to them. For example, the pleasant odor of freshly baked bread might smell overpowering and rotten instead of subtle and sweet.

People experience a wide range of parosmia for an array of different reasons. In the most severe cases, parosmia can cause you to feel physically ill when your brain detects strong, unpleasant scents.

Most cases of parosmia become apparent after you recover from an infection. Symptom severity varies from case to case.

If you have parosmia, your main symptom would be sensing a persistent foul odor, especially when food is around. You may also have difficulty recognizing or noticing some scents in your environment, a result of damage to your olfactory neurons.

Scents that you used to find pleasant may now become overpowering and unbearable. If you try to eat food that smells bad to you, you may feel nauseous or sick while you’re eating.

Parosmia usually occurs after your scent-detecting neurons — also called your olfactory senses — have been damaged due to a virus or other health condition. These neurons line your nose and tell your brain how to interpret the chemical information that makes up a smell. Damage to these neurons changes the way smells reach your brain.

The olfactory bulbs underneath the front of your brain receive signals from these neurons and give your brain a signal about the scent: whether it’s pleasing, enticing, appetizing, or foul. These olfactory bulbs can be damaged, which can cause parosmia.

Head injury or brain trauma

Traumatic brain injury (TBI) has been linked to olfactory damage. While the duration and severity of the damage depends on the injury, a review of medical literature indicated that symptoms of parosmia after a TBI are not uncommon.

TBI can also lead to a loss of sense of smell from shearing of the olfactory nerve fibers at the cribriform plate. Brain trauma can also be caused by damage from a seizure, leading to parosmia.

Bacterial or viral infection

One cause of parosmia symptoms is olfactory damage from a cold or virus. Upper respiratory infections can damage the olfactory neurons. This happens more often in older adults.

In a 2005 study of 56 people with parosmia, just over 40 percent of them had an upper respiratory infection they believed was connected to the onset of the condition.

Smoking and chemical exposure

Your olfactory system can sustain damage from smoking cigarettes. The toxins and chemicals in cigarettes can cause parosmia over time.

For this same reason, exposure to toxic chemicals and high volumes of air pollution can cause parosmia to develop.

Cancer treatment side effect

Radiation and chemotherapy can cause parosmia.

A 2016 review found that 86 percent of cancer patients reported changes in their sense of smell and taste while undergoing treatment. In one case study from 2006, this side effect led to weight loss and malnutrition due to food aversions connected to parosmia.

Neurological conditions

One of the first symptoms of Alzheimer’s disease and Parkinson’s disease is a loss of the sense of smell. Lewy body dementia and Huntington’s disease also cause difficulty in sensing smells properly.

Tumors

Tumors on the olfactory bulbs, in the frontal cortex, and in your sinus cavities can cause changes to your sense of smell. It’s rare for a tumor to cause parosmia.

More often, people who have tumors experience phantosmia — the detection of a scent that is not present because of a tumor triggering the olfactory senses.

COVID-19 infection

While COVID-19 has been associated with a loss of smell (anosmia) in some people, it’s also possible to experience parosmia after having the viral infection. It’s thought that the virus makes changes to the olfactory system, where sustained damage may change the way you smell after recovery.

One 2021 study of two adults recovering from COVID-19 report such changes. First, a 28-year-old male reported smelling burnt rubber after recovering from anosmia, which occurred 87 days after getting sick. Another adult, a 32-year-old female, reported smelling onions after 72 days.

Such cases point to parosmia as a possible long-term complication of COVID-19. Researchers of this study note that COVID-19–related parosmia is considered rare, and other medical professionals point out that parosmia after COVID-19 is a sign that your olfactory system may be recovering.

Since the effects of this coronavirus on your olfactory system are still being researched, it’s important to know that information about short-term and long-term effects on your sense of smell are still coming to light.

At the same time, parosmia as part of your COVID-19 recovery can be difficult, as it may change your enjoyment of and desire for certain foods. You may also consider discussing olfactory retraining with your doctor.

Parosmia can be diagnosed by an otolaryngologist, also known as an ear-nose-throat doctor, or ENT. The doctor may present different substances to you and ask you to describe their scent and rank their quality.

A common test for parosmia involves a small booklet of “scratch and sniff” beads that you respond to under a doctor’s observation.

During the appointment, your doctor may ask questions about:

  • your family history of cancer and neurological conditions
  • any recent infections you’ve had
  • lifestyle factors such as smoking
  • medications you currently take

If your doctor suspects that the underlying cause of your parosmia could be neurological or cancer-related, they may suggest further testing. This could include a:

  • sinus CT
  • biopsy of the sinus region
  • an MRI

Parosmia can be treated in some, but not all, cases. If parosmia is caused by environmental factors, medication, cancer treatment, or smoking, your sense of smell may return to normal once those triggers are removed.

Sometimes surgery is required to resolve parosmia. Nasal obstructions, such as polyps or tumors, may need to be removed.

Treatments for parosmia include:

  • zinc
  • vitamin A
  • antibiotics

More research and case studies are needed to prove these are more effective than placebo.

If you continue to experience parosmia and it’s impacting your appetite and weight, you may consider olfactory training therapy. Also known as “smell training,” this type of therapy involves intentionally sniffing four different types of odors up to 15 seconds at a time each. The process is completed twice daily for several months.

You’ll need to speak with your doctor to find out the best treatment for you.

Parosmia is not typically a permanent condition. Your neurons may be able to repair themselves over time. In as many as 60 percent of cases of parosmia caused by an infection, olfactory function was restored in the years afterward.

Recovery times vary according to the underlying cause of your parosmia symptoms and the treatment that you use. If your parosmia is caused by a virus or infection, your sense of smell may return to normal without treatment. Olfactory training may potentially help with recovery, but it may take several months to see results.

Parosmia can usually be traced back to an infection or brain trauma. When parosmia is triggered by medication, chemical exposure, or smoking, it usually subsides once the trigger is removed.

Less often, parosmia is caused by a sinus polyp, a brain tumor, or is an early sign of certain neurological conditions.

Age, gender, and how good your sense of smell was to begin with all play a part in the long-term prognosis for people with parosmia.

Speak with your doctor if you experience any changes in the way that you experience smell.