Loss of Smell: Causes and How to Get It Back

How smell works

Odor molecules travel to a small patch of tissue high in the nose (the olfactory cleft), where smell nerve cells send signals through tiny holes in the skull to the olfactory bulb and brain. Smell can be lost when:

• air cannot reach the smell area (conductive loss): congestion, polyps, swelling
• the smell nerve cells are damaged (sensorineural loss): viruses, injury, toxins, aging
• the brain pathways are affected: head injury, neurological disease

Most of what people call "taste" is actually flavor detected by smell. True taste (sweet, salty, sour, bitter, umami) on the tongue usually remains.

Causes of loss of smell

Viral infections

• Common cold and flu: congestion blocks smell temporarily; some viruses also damage smell cells.
• COVID-19: sudden loss of smell, often without a blocked nose, was a hallmark of early variants and is less common with later ones. Most recover within weeks, but a minority have lasting loss or distorted smell (parosmia).

Nose and sinus disease

• Chronic sinusitis: blocked nose, thick discharge and facial pressure for 12 weeks or more.
• Nasal polyps: soft growths in the nose and sinuses, often with asthma; smell loss is a typical early symptom.
• Allergic rhinitis: swelling during allergy seasons.
• Deviated septum or a nasal tumor: one-sided blockage.

Head injury

A blow to the head, even a mild one, can shear the delicate smell nerve fibers. Loss may be permanent, though some improvement can happen over 1 to 2 years.

Aging

Smell declines naturally with age. A large share of people over 65, and most over 80, have some measurable loss. This affects appetite and the ability to detect smoke, gas leaks and spoiled food.

Neurological disease

Smell loss can be one of the earliest signs of Parkinson's disease, appearing years before tremor or stiffness, and of Alzheimer's disease. Smell loss by itself does not mean you have these conditions, as many other causes are far more common.

Other causes

• Smoking and vaping.
• Medicines: some antibiotics, blood pressure drugs, and overuse of decongestant sprays; zinc nasal gels have been linked to permanent loss.
• Chemical and toxic exposures: solvents, pesticides, heavy metals.
• Radiation therapy to the head and neck.
• Hormonal and metabolic conditions: hypothyroidism, diabetes, kidney and liver disease.
• Congenital anosmia: being born without a sense of smell, including Kallmann syndrome with delayed puberty.

See also anosmia for more on the condition itself.

Related smell changes

• Parosmia: familiar smells become distorted and often unpleasant (coffee smells like burning or garbage). Common during recovery after viral infection.
• Phantosmia: smelling things that are not there, such as smoke. It can follow viral infection and, rarely, reflects seizures or brain lesions.

How doctors diagnose the cause

A doctor or ENT specialist will ask when the loss started, whether it was sudden or gradual, about colds, COVID-19, injury, nasal symptoms, medicines and neurological symptoms. They will examine the nose, often with a thin camera (nasal endoscopy) to look for polyps or swelling.

• Smell testing: scratch-and-sniff tests (such as the UPSIT) or sniffing pens measure how much smell is lost.
• CT scan of the sinuses: for chronic sinusitis or polyps.
• MRI of the brain: if there is no nasal cause, after a head injury, or with neurological symptoms.

Treatment

Treat the cause

• Congestion, allergies and sinusitis: saline rinses and steroid nasal sprays; a short course of oral steroids may be used for polyps.
• Nasal polyps: steroid sprays, surgery and, for severe cases, biologic medicines.
• Medicines: your doctor may adjust a drug that affects smell.
• Stop smoking: smell often improves within months.

Smell training (olfactory training)

Smell training is the best-supported treatment for loss after viral infection or head injury.

1. Choose 4 distinct scents, traditionally rose, lemon, clove and eucalyptus.
2. Twice a day, sniff each one gently for about 20 seconds while concentrating on the memory of that smell.
3. Continue for at least 3 to 6 months, switching to new scents after a few months.

Staying safe

• Fit smoke and carbon monoxide detectors and test them regularly.
• Use gas detectors if you have gas appliances.
• Label and date food, and follow use-by dates.
• Ask someone else to check for smells such as gas or burning when unsure.

Frequently asked questions

What causes sudden loss of smell?

Sudden smell loss is usually caused by a viral infection, including COVID-19 or a cold, or by a head injury. Severe nasal congestion from allergies or sinusitis can also cause it. If smell does not return within a few weeks, see a doctor.

How long does loss of smell last?

After a cold, smell usually returns within 1 to 3 weeks. After COVID-19, most people recover within a few weeks to months, but some take a year or more. Loss after head injury may improve slowly over 1 to 2 years or be permanent.

Why have I lost my sense of smell and taste?

Most of what we call taste is actually smell, so smell loss makes food taste bland. True taste on the tongue (sweet, salty, sour, bitter) usually works. Losing both at once most often follows a viral infection or comes from nasal congestion.

Does smell training work?

Yes, for many people. Studies show that sniffing 4 strong scents twice daily for several months improves recovery after viral infections and head injuries. It is safe, cheap and recommended by ENT specialists for post-viral smell loss.

Can loss of smell be a sign of something serious?

Usually it is not. Gradual smell loss with no nasal cause can be an early sign of Parkinson's or Alzheimer's disease, and one-sided nasal blockage with smell loss can rarely be a tumor. A doctor can examine your nose and arrange tests if needed.