How does the sense of smell work?
The sense of smell is a part of one’s chemical senses or chemosensory system. One has the ability to smell due to the presence of olfactory sensory neurons (specialized sensory cells). Every individual olfactory neuron has an odor receptor. The substances around one release microscopic molecules. These microscopic molecules perform the function of stimulating the odor receptors.
Microscopic molecules in the air are breathed by one which passes through the nose. Inside the nasal cavity, it is funneled to the olfactory epithelium (tissue). Located in line with the top of the cheekbones, these small clusters of cells are covered with cilia (tiny hairs) and a thin layer of mucus. The cilia aids in trapping the inhaled microscopic molecules.
The messages of the microscopic molecules are detected by the olfactory neurons. The olfactory neurons then relay the information via the nervous system to the brain. The brain processes and identifies the smell.
The environment contains more smells in it, than one has receptors. One molecule can arouse a group of receptors which creates a unique representation in the brain. The brain helps in registering these representations as a distinct smell.
There are mainly two routes through which smells reach one’s olfactory sensory neurons:
- Through one’s nostrils
- Through a passage connecting one’s nose with the roof of the throat
Can day-to-day elements reduce the sense of smell?
The sense of smell can be reduced by day-to-day elements like:
- Smoking – The sense of smell diminishes especially for half an hour after smoking a cigarette.
- Nasal mucus – Nasal mucus which is caused by a number of medical conditions such as cold, influenza, allergic rhinitis or sinusitis dampens the sense of smell.
- Adaptation – This situation occurs when the olfactory receptors are flooded to the point of saturation with certain odor molecules.
What are the factors that disturb the sense of smell?
The sense of smell tend to get disturbed by the following factors:
A wide variety of industrial chemicals along with heavy metals, inorganic and organic compounds, acids and containments.
Disorders of the hormonal system like diabetes, Cushing’s syndrome and hypothyroidism.
Disorders of the nervous system like Alzheimer’s disease, multiple sclerosis, migraine, Korsakoff syndrome, brain tumors, brain lesions and epilepsy.
Drugs like stimulants, depressants, few antibiotics and other drugs. Also vasoconstrictors in nasal spray are included.
Diseases like bronchial asthma, leprosy and cystic fibrosis.
Traumas include blows to the head or injuries to the nose.
What does it mean by loss of smell?
Any kind of problem in the process of olfactory neurons detecting and sending messages to the brain can result in a loss of smell. A stuffy nose, blockage, inflammation, nerve damage or a brain function condition can naturally affect one’s ability to smell. Apart from these, there are several medications, diseases, hormonal disturbances and chemicals that can disturb the sense of smell, sometimes permanently.
Anosmia is a medical condition which is defined as a complete loss of smell. While hyposmia is the condition of partial loss of smell.
One suffering with the condition of anosmia tends to taste salty, sweet, sour and bitter substances. But he/she can not differentiate between certain flavors. The ability to differentiate between flavors depends on smell. It is a common complaint among those suffering from anosmia, that he/she can not enjoy their food after losing the sense of smell.
For most individuals, anosmia is a temporary condition triggered by a seriously stuffy nose from a cold. They will get back their sense of smell, after the cold gets cured. But for some, including many seniors, the condition of loss of smell is persistent and could actually indicate a more critical health condition.
The most common causes of extended loss of smell arises as a result of upper respiratory infection and sinusitis.
What causes loss of smell?
The main causes of loss of smell can be categorized as:
This can arise from:
- Sinus infections
- Common colds
- Smoking
- Flu or influenza
- Allergic rhinitis
- Non allergic rhinitis
This can arise from:
- Tumors
- Nasal polyps
- Bone deformities inside the nose or a nasal septum
This includes:
- Old age
- Alzheimer’s disease
- Brain tumors
- Hungtinton’s disease
- Hormonal problems
- Underactive thyroid
- Medications
- Multiple sclerosis
- Parkinson’s disease
- Schizophrenia
- Epilepsy
- Diabetes
- Exposure to chemical substances that burn the inside of the nose
- Brain to head injury
- Brain surgery
- Malnutrition and vitamin deficiencies
- Radiation therapy
- Long-term alcoholism
- Stroke
How is sinusitis related to loss of smell?
Sinusitis is the medical condition where one suffers from swelling of the sinuses, generally triggered by an infection. It causes swelling and inflammation of one’s sinuses which tends to disrupt mucus drainage.
The symptoms of sinusitis includes:
- Blocked nose
- Swelling
- Tenderness around eyes, cheeks or forehead
- Toothache
- Sinus headache
- Discharge of yellow or green mucus
- Bad breath
- High temperature
- Decreased sense of smell
Air movement in the sinuses generally aids the unsteady molecules to settle in, providing a brain signal letting one know what he/she is tasting. Therefore, a sinus infection could make one’s sense of taste dull.
One is likely to suffer from sinusitis, if he/she has:
- Abnormalities with the nasal passage
- Deviated nasal septum or tumors
- Allergic reactions affection sinuses
- Exposure to smoke
- Immune system disorders (like HIV/AIDs or cystic fibrosis)
How is loss of smell treated?
The treatment of loss of smell depends on its underlying cause. A loss of smell, caused by sinus infection or sinusitis can be treated with:
- Decongestants
- Antihistamines
- Steroid nasal sprays
- Antibiotics (for bacterial infections)
- Limiting exposure to nasal irritants and allergens
- Discontinuation of smoking
In some instances, a surgery is required to treat the loss of smell.
Diagnosis, complications and precautions related to loss of smell
It is difficult to measure the loss of smell. One’s ENT physician may ask him/her a few questions about their current symptoms and medical history. The ENT physicians will also examine one’s nose and perform a complete physical examination.
Some of the tests an ENT physician may carry out includes:
- CT scans
- MRI scans
- X-ray of the skull
- Nasal endoscopy
A loss of smell may give rise to the following complications in one:
- An inability to taste food, which can result in eating too much or too little
- An inability to smell spoiled food, which can result in food poisoning
- Increased danger in case of fire events
- An inability to recollect smell-related memories
- An inability detect chemicals or other dangerous odors in the home
- Lack of empathy from family, friends or doctors
- An inability to detect body odors
- Mood disorders like depression
Some suggested precautions one can follow to deal with the loss of smell are:
- Duly labeling all foods with expiration dates
- Use electric appliances
- Carefully read labels on chemicals (like insecticides and kitchen cleaners)
