Parosmia: What illness makes everything smell bad?

September 21, 2025 •

4 min read

According to research, a significant number of individuals who recover from respiratory infections like COVID-19 go on to experience parosmia, the illness that makes everything smell bad. This condition distorts familiar scents, turning pleasant smells into foul or unpleasant odors.

Quick Summary

The medical term for when everything smells bad is parosmia, a distortion of the sense of smell often triggered by nerve damage from viral infections, head injuries, or other neurological conditions. It can cause familiar and pleasant scents to be perceived as foul or repulsive.

Key Points

Parosmia is a distorted sense of smell: This condition causes existing odors to be perceived differently and often as foul, burnt, or chemical smells.
Viral infections are a leading cause: Upper respiratory infections, especially COVID-19, are frequent triggers for parosmia by damaging the olfactory nerves.
It differs from phantosmia: Unlike phantosmia, where phantom smells are perceived without a stimulus, parosmia requires a real external odor to trigger the distorted perception.
Recovery can take time: The distorted smells often occur during the regeneration phase of the olfactory nerves and can gradually improve over months or years.
Olfactory training is a key therapy: Regularly smelling specific scents is a simple, effective method to help retrain the brain's interpretation of odors.
Impacts on life can be severe: Parosmia can lead to reduced appetite, malnutrition, depression, and social anxiety, as well as compromise safety.

Understanding Parosmia, the 'Bad Smell' Illness

Parosmia is a qualitative olfactory disorder, a condition that alters or distorts a person's sense of smell. Instead of a complete loss of smell (anosmia), parosmia causes the brain to misinterpret and distort odors, often making them smell unpleasant, rotten, or metallic. This can have a significant impact on a person’s quality of life, affecting appetite, mood, and overall safety by masking important warning smells. The distorted smell perception is often a sign of regeneration in the olfactory system, but sometimes the rewiring is abnormal, leading to the perception of foul smells instead of the original scent.

What Causes Parosmia?

The root cause of parosmia is damage to the olfactory system, the network of nerve cells and brain structures responsible for interpreting smells. When these nerves are damaged, they may not regenerate properly, leading to a misinterpretation of scent signals by the brain. Common causes include:

Viral Infections

COVID-19: Since the onset of the pandemic, COVID-19 has become one of the most well-known causes of parosmia. Many people who initially lost their sense of smell experienced parosmia during the recovery phase, with distorted smells lasting for months or even over a year.
Upper Respiratory Infections (URIs): Common colds, influenza, and other viral infections can cause inflammation and damage to the olfactory neuroepithelium, which can lead to parosmia.

Head Trauma

A traumatic brain injury, such as from a concussion or accident, can cause shearing of the olfactory nerves as the brain moves inside the skull. The recovery of these nerves is not always perfect, which can result in distorted smells.

Neurological Conditions

Parkinson's Disease and Alzheimer's Disease: A diminished or distorted sense of smell can be an early symptom of these neurodegenerative conditions.
Brain Tumors: Tumors, especially in the frontal lobe or on the olfactory bulb, can interfere with smell processing and cause olfactory issues.
Temporal Lobe Seizures: Episodes of seizures can sometimes cause olfactory hallucinations or distortions.

Other Factors

Chemical Exposure: Long-term exposure to certain toxins, such as paint thinners, cleaning solvents, or other industrial chemicals, can damage olfactory nerves.
Certain Medications: Some drugs, including chemotherapy agents, antibiotics, and antidepressants, are known to alter the sense of smell.
Smoking: Tobacco smoke is a significant irritant to the olfactory system and can cause progressive damage over time.
Aging: As people age, a natural decline in olfactory function can occur, increasing the likelihood of developing a smell disorder.

Differentiating Parosmia from Other Smell Disorders

It is important to distinguish between different types of smell disorders, as each has a unique profile. Parosmia is often confused with phantosmia, but a key difference is the presence of an external odor stimulus.


Feature	Parosmia (Distorted Smell)	Phantosmia (Phantom Smell)
Definition	An existing odor smells different than it should, usually foul.	Perceiving a smell when no odor is present.
Trigger	Requires a real-world odorant stimulus (e.g., food, coffee, perfume).	Can occur without any external stimulus, like a hallucination.
Timing	Often appears during recovery from a viral infection or head injury.	Can be triggered by head trauma, seizures, or stress.
Description	Formerly pleasant smells become burnt, rotten, or sewage-like.	Smells often described as smoke, burning, or chemical.
Prognosis	Tends to improve over time as nerves regenerate.	Less likely to show spontaneous improvement.

Coping with and Treating Parosmia

While parosmia can be very distressing, several strategies and treatments can help manage symptoms and aid recovery.

Olfactory Training (Smell Training)

This is a widely recommended, non-invasive method to help retrain the sense of smell, particularly after viral infections.

Select four distinct scents: Choose pleasant, strong scents, such as rose, eucalyptus, lemon, and cloves, using essential oils or natural sources.
Sniff daily: Sniff each scent for 15-30 seconds, twice a day, typically in the morning and evening.
Focus on memory: As you sniff, concentrate on what the scent is supposed to smell like, helping to rebuild the correct neural pathways.
Be patient: It can take several months to a year or more to see significant improvement.

Other Supportive Measures

Address underlying causes: If the parosmia is caused by a treatable condition like a sinus infection or nasal polyps, a doctor may recommend medication or surgery.
Dietary adjustments: Experiment with different foods and cooking methods. Cold or room-temperature foods may be less triggering than hot, steaming dishes, as the steam carries more odor molecules.
Avoid triggers: Identify and avoid specific smells that cause a strong negative reaction. Common triggers include coffee, onions, garlic, and cooked meat.
Lifestyle changes: Quitting smoking and avoiding chemical exposure can prevent further damage to the olfactory system.
Mental health support: Living with parosmia can lead to frustration, anxiety, and depression. Seeking therapy or joining support groups can help.

Medical and Surgical Treatments

In some cases, a healthcare provider may suggest other treatments:

Medication: Some studies suggest that certain medications, such as intranasal steroids, may help with smell disorders, though more research is needed. Antiepileptic drugs have also been explored for neurological-related cases.
Surgery: For cases caused by structural problems like tumors or polyps, surgical removal may resolve the issue. In very rare and severe cases, ablation of the olfactory epithelium has been performed, though this results in permanent anosmia.

Conclusion

Parosmia is a challenging condition that fundamentally alters the perception of smell, but it is often a sign of recovery rather than permanent damage. For individuals asking what illness makes everything smell bad, identifying it as parosmia is the first step toward understanding the condition. Managing symptoms through olfactory training, dietary adjustments, and addressing the underlying cause can help mitigate its impact. While patience is required for the olfactory system to heal, the prognosis for recovery is generally positive. Always consult a healthcare professional for a proper diagnosis and treatment plan. For more detailed information on olfactory disorders, visit the Cleveland Clinic website.

Frequently Asked Questions

The duration varies depending on the cause and individual. For post-viral parosmia, it can last from several months to over a year, but in many cases, it improves significantly over time.

While stress is not a direct cause, the anxiety and frustration associated with parosmia can affect one's perception of the condition. Emotional distress can heighten awareness of the unpleasant smells, making the symptoms feel more intense.

Yes, COVID-19 is a major cause of parosmia. The virus can damage the nerve cells in the olfactory system, and parosmia often develops as these nerves begin to regenerate incorrectly months after the initial infection.

Food triggers can be highly individual, but common offenders include coffee, cooked meat, onions, and garlic. The heat from cooking often intensifies the odors, making cold or room-temperature foods more tolerable.

There is no single cure, but many cases resolve on their own as the olfactory nerves heal. Treatments like olfactory training can speed up recovery. For some, managing the underlying cause, like a sinus infection, is the key to resolution.

Olfactory training involves regularly sniffing a series of strong scents, like rose, lemon, and eucalyptus, while concentrating on remembering their true smell. This helps stimulate and retrain the brain's olfactory pathways to correctly interpret scents again.

You should see a healthcare provider anytime you experience a sudden or persistent change in your sense of smell. They can help diagnose the underlying cause, rule out more serious conditions like brain tumors, and recommend appropriate treatment.