How do taste and smell work?
- Taste and smell belong to our chemical sensing system
- The complicated process of smelling and tasting begins when molecules released by the substances around us stimulate special nerve cells in the nose, mouth, or throat
- These cells transmit messages to the brain, where specific smells or tastes are identified
- Our body’s ability to sense chemicals is another chemosensory mechanism that contributes to our senses of smell and taste
- In this system, thousands of free nerve endings—especially on the moist surfaces of the eyes, nose, mouth, and throat
- Taste and smell allows us to identify sensations like the sting of ammonia, the coolness of menthol, and the “heat” of chili peppers
The sense of smell
- Olfactory (smell nerve) cells are stimulated by the odours around us, for example. the fragrance from a rose, the smell of bread baking
- These nerve cells are found in a tiny patch of tissue high up in the nose, and they connect directly to the brain
The sense of taste
- Gustatory (taste nerve) cells are clustered in the taste buds of the mouth and throat
- They react to food or drink mixed with saliva
- Many of the small bumps that can be seen on the tongue contain taste buds
- These surface cells send taste information to nearby nerve fibres, which send messages to the brain
What causes loss of taste and smell?
Aging
- Scientists have found that the sense of smell is most accurate between the ages of 30 and 60 years
- It begins to decline after age 60, and a large proportion of elderly persons lose their smelling ability
Gender
- Women of all ages are generally more accurate than men in identifying odours
Genetics
- Some people are born with a poor sense of taste and smell
Cold and flu
- Upper respiratory infections are blamed for some losses, and injury to the head can also cause taste and smell problems
Chronic sinusitis and nasal polyps
- Loss of taste and smell may result from polyps in the nasal or sinus cavities
Irritants and chemicals
- Loss of taste and smell can also be caused by prolonged exposure to certain chemicals such as insecticides, and by some medicines
- Tobacco smoking is the most concentrated form of pollution that most people are exposed to – it impairs the ability to identify odours and diminishes the sense of taste
- Quitting smoking improves the taste and smell function
Head and neck causes
- Radiation therapy patients with cancers of the head and neck often report loss of smell and taste – these senses can also be lost in the course of some diseases of the nervous system
- Patients who have lost their larynx (voice box) commonly report poor ability to smell and taste
- Laryngectomy patients can use a special “bypass” tube to breathe through the nose again – the enhanced air flow through the nose helps smell and taste sensations to be re-established
How are loss of taste and smell diagnosed?
- The extent of loss of smell or taste can be tested using the lowest concentration of a chemical that a person can detect and recognize
- A patient may also be asked to compare the smells or tastes of different chemicals, and how the intensities of smells and tastes grow when a chemical concentration is increased
- Smell — Scientists have developed an easily administered “scratch-and-sniff” test to evaluate the sense of smell
- Taste — Patients react to different chemical concentrations in taste testing; this may involve a simple “sip, spit, and rinse” test, or chemicals may be applied directly to specific areas of the tongue
Can these disorders be treated?
- Sometimes certain medications are the cause of smell or taste disorders, and improvement occurs when that medicine is stopped or changed
- Although certain medications can cause chemosensory problems, others—particularly anti-allergy drugs—seem to improve the senses of taste and smell
- Some patients, notably those with serious respiratory infections or seasonal allergies, regain their smell or taste simply by waiting for their illness to run its course
- In many cases, nasal obstructions, such as polyps, can be removed to restore airflow to the receptor area and can correct the loss of smell and taste
- Occasionally, the sense of taste and smell return to normal just as spontaneously as they disappeared
How do you cope with taste and smell problems?
- If you experience problems in smelling or tasting, try to identify and record the circumstances surrounding it:
- When did you first become aware of it?
- Did you have a cold or flu then?
- A head injury?
- Were you exposed to air pollutants, pollens, danders, or dust to which you might be allergic?
- Is this a recurring problem?
- Does it come in any special season, like hayfever time?
Management of smell and taste problems
- Bring the details regarding your symptoms with you when you visit an ENT specialist who deals with diseases of the nose and throat (an otolaryngologist—head and neck surgeon)
- Proper diagnosis by an experienced ENT specialist can provide reassurance that your illness is not imaginary
- You may even be surprised by the results
- For example, what you may think is a taste problem could actually be a smell problem, because much of what you taste is really caused by smell
- Diagnosis may also lead to treatment of an underlying cause for the disturbance – remember, many types of smell and taste disorders are reversible.
Flavour
- Four commonly identified taste sensations:
- sweet
- sour
- bitter
- salt
- Certain tastes combine with texture, temperature, and odour to produce a flavour that allows us to identify what we are eating
- Many flavours are recognized through the sense of smell
- If you hold your nose while eating chocolate, for example, you will have trouble identifying the chocolate flavour, even though you can distinguish the food’s sweetness or bitterness
- This is because the familiar flavour of chocolate is sensed largely by odour
- So is the well known flavour of coffee
- This is why a person who wishes to fully enjoy a delicious flavour (e.g., an expert chef testing his own creation) will exhale through his nose after each swallow
Natural regeneration of taste and smell nerves
- Taste and smell cells are the only cells in the nervous system that are replaced when they become old or damaged
- Scientists are examining this phenomenon while studying ways to replace other damaged nerve cells
