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 traumatic brain injury aren’t uncommon. Brain trauma can also be caused by damage from having 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 populations.

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. 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 your sense of smell. Lewy body dementia and Huntington’s disease also bring on difficulty in sensing smells properly.

Tumors

Tumors on the sinus 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 isn’t present because of a tumor triggering the olfactory senses.

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 for 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 X-ray, biopsy of the sinus region, or 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:

  • a nose clip to prevent smells from entering your nose
  • zinc
  • vitamin A
  • antibiotics

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

Some people with parosmia find their symptoms subside with “smell gymnastics,” in which they expose themselves to four different kinds of scents each morning and try to train their brain to categorize those scents appropriately.

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

Parosmia isn’t 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. But on average, this takes between two and three years.

In a small study from 2009, 25 percent of people who took part in a 12-week “smelling gymnastics” exercise improved their parosmia symptoms. More research is needed to understand whether this kind of treatment is effective.

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