Smell Disorders: Parosmia, Anosmia, Phantosmia & Hyposmia

Smell disorder facts*

*Smell disorder facts by John P. Cunha, DO, FACOEP

People who experience smell disorders experience either a loss in their ability to smell or changes in the way they perceive odors.
Hyposmia is when the ability to detect odor is reduced. Anosmia is when a person can't detect odor at all. Some people experience change in the perception of odors, or notice that familiar odors become distorted, or may perceive a smell that isn't present at all.
Smell disorders have many causes including illness such as upper respiratory infection, injury, polyps in the nasal cavities, sinus infections, hormonal disturbances, dental problems, exposure to certain chemicals such as insecticides and solvents, some medicines, and radiation due to head and neck cancers.
Obesity, diabetes, hypertension, malnutrition, Parkinson's disease, Alzheimer's disease, multiple sclerosis, and Korsakoff's psychosis are all accompanied or signaled by chemosensory problems like smell disorders.
There is no specific treatment for smell disorders. If the cause is due to medication, adjusting or changing the drug may relieve symptoms. If an underlying illness causes the smell disorder, when that illness resolves or is treated the sense of smell usually returns. Surgery can remove nasal polyps.

Every year, thousands of people develop problems with their sense of smell. In fact, more than 200,000 people visit a physician each year for help with smell disorders or related problems. If you experience a problem with your sense of smell, call your doctor. This fact sheet explains smell and smell disorders.

Many people who have smell disorders also notice problems with their sense of taste.

What Causes a Loss of Smell?

Anosmia is the medical term that refers to the loss of sense of smell. The sensations of taste and smell are related, so many disorders of the sense of smell are also associated with a decreased sense of taste. Causes of loss of sense of smell vary and can range from

infections,
obstructions in or damage to the nose,
to damage to the brain and nervous system in general.

Anosmia may be temporary, as occurs with some infections, or permanent. Irritation to the mucus membranes of the nose from smoking, inhalation of pollutants or toxins, or from infections can affect the ability to perceive smells.

Some loss of sense of smell occurs during normal aging. Sometimes, having a cold, sinus infection, or the flu can result in a decrease in the ability to perceive smells. An infection with the recently described virus SARS-CoV-2 (COVID-19) has also been reported to cause a loss of the sense of smell.

Learn about the various causes of a loss of sense of smell (anosmia) »

How does your sense of smell work?

Your sense of smell — like your sense of taste — is part
of your chemosensory system, or the chemical senses.

Your ability to smell comes from specialized sensory
cells, called olfactory sensory neurons, which are
found in a small patch of tissue high inside the nose.
These cells connect directly to the brain. Each olfactory
neuron has one odor receptor. Microscopic molecules
released by substances around us — whether it’s coffee
brewing or pine trees in a forest — stimulate these
receptors. Once the neurons detect the molecules,
they send messages to your brain, which identifies
the smell. There are more smells in the environment
than there are receptors, and any given molecule may
stimulate a combination of receptors, creating a unique
representation in the brain. These representations are
registered by the brain as a particular smell.

Smells reach the olfactory sensory neurons through two
pathways. The first pathway is through your nostrils. The
second pathway is through a channel that connects the
roof of the throat to the nose. Chewing food releases
aromas that access the olfactory sensory neurons through
the second channel. If the channel is blocked, such as
when your nose is stuffed up by a cold or flu, odors can’t
reach the sensory cells that are stimulated by smells. As
a result, you lose much of your ability to enjoy a food’s
flavor. In this way, your senses of smell and taste work
closely together.

Without the olfactory sensory neurons, familiar
flavors such as chocolate or oranges would be hard to
distinguish. Without smell, foods tend to taste bland
and have little or no flavor. Some people who go to the doctor because they think they’ve lost their sense of
taste are surprised to learn that they’ve lost their sense of
smell instead.

Your sense of smell is also influenced by something
called the common chemical sense. This sense involves
thousands of nerve endings, especially on the moist
surfaces of the eyes, nose, mouth, and throat. These
nerve endings help you sense irritating substances — such
as the tear-inducing power of an onion — or the refreshing
coolness of menthol.

What are the smell disorders?

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People who have a smell disorder either have a decrease
in their ability to smell or changes in the way they
perceive odors.

Hyposmia [high-POSE-mee-ah] is a reduced ability to
detect odors.
Anosmia [ah-NOSE-mee-ah] is the complete inability
to detect odors. In rare cases, someone may be
born without a sense of smell, a condition called
congenital anosmia.
Parosmia [pahr-OZE-mee-ah] is a change in the normal
perception of odors, such as the smell of something
familiar is distorted, or something that normally smells
pleasant now smells foul.
Phantosmia [fan-TOES-mee-ah] is the sensation of an
odor that isn’t there.

How common are smell disorders?

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Your sense of smell helps you enjoy life. You may delight
in the aromas of your favorite foods or the fragrance of
flowers. Your sense of smell is also a warning system,
alerting you to danger signals such as a gas leak, spoiled
food, or a fire. Any loss in your sense of smell can have a
negative effect on your quality of life. It can also be a sign
of more serious health problems.

One to two percent of North Americans report problems
with their sense of smell. Problems with the sense of smell
increase as people get older, and they are more common
in men than women. In one study, nearly one-quarter of
men ages 60 to 69 had a smell disorder, while about 11
percent of women in that age range reported a problem.

Many people who have smell disorders also notice problems with their sense of
taste.

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What causes smell disorders?

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Smell disorders have many causes, with some more
obvious than others. Most people who develop a smell
disorder have experienced a recent illness or injury.
Common causes of smell disorders are:

Aging
Sinus and other upper respiratory infections
Smoking
Growths in the nasal cavities
Head injury
Hormonal disturbances
Dental problems
Exposure to certain chemicals, such as insecticides and
solvents
Numerous medications, including some common
antibiotics and antihistamines
Radiation for treatment of head and neck cancers
Conditions that affect the nervous system, such as
Parkinson’s disease or Alzheimer’s disease.

How are smell disorders diagnosed and treated?

Both smell and taste disorders are treated by an otolaryngologist, a doctor who specializes in diseases of the ear, nose, throat, head, and neck (sometimes called an ENT). An accurate assessment of a smell disorder will include, among other things, a physical examination of the ears, nose, and throat; a review of your health history, such as exposure to toxic chemicals or injury; and a smell test supervised by a health care professional.

There are two common ways to test smell. Some tests are designed to measure the smallest amount of odor that someone can detect. Another common test consists of a paper booklet of pages that contain tiny beads filled with specific odors. People are asked to scratch each page and identify the odor. If they can't smell the odor, or identify it incorrectly, it could indicate a smell disorder or an impaired ability to smell.

Diagnosis by a doctor is important to identify and treat the underlying cause of a potential smell disorder. If your problem is caused by medications, talk to your doctor to see if lowering the dosage or changing the medicine could reduce its effect on your sense of smell. If nasal obstructions such as polyps are restricting the airflow in your nose, you might need surgery to remove them and restore your sense of smell.

Some people recover their ability to smell when they recover from the illness causing their loss of smell. Some people recover their sense of smell spontaneously, for no obvious reason. If your smell disorder can't be successfully treated, you might want to seek counseling to help you adjust.

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Are smell disorders serious?

Like all of your senses, your sense of smell plays an
important part in your life. Your sense of smell often
serves as a first warning signal, alerting you to the smoke
of a fire, spoiled food, or the odor of a natural gas leak or
dangerous fumes.

When their smell is impaired, some people change their
eating habits. Some may eat too little and lose weight
while others may eat too much and gain weight. As food
becomes less enjoyable, you might use too much salt to
improve the taste. This can be a problem if you have or
are at risk for certain medical conditions, such high blood
pressure or kidney disease. In severe cases, loss of smell
can lead to depression.

Problems with your chemical senses may be a sign of
other serious health conditions. A smell disorder can
be an early sign of Parkinson’s disease, Alzheimer’s
disease, or multiple sclerosis. It can also be related to
other medical conditions, such as obesity, diabetes,
hypertension, and malnutrition. If you are experiencing a
smell disorder, talk with your doctor.