Sense of smell and sense of taste – how are they related?

Smells accompany people, even more than taste, throughout their lives. Smells not only convey information but also influence feelings. A pleasant or unpleasant smell or taste warns people, triggers well-being or conveys pleasure. The sense of smell and the sense of taste are closely related. Around 50,000 people in Germany suffer from disorders of their sense of smell and taste every year – for example with sinusitis or Parkinson’s disease. Even a simple sniffle can significantly impair sensation. However, an infection with the coronavirus can also lead to a loss of smell and taste, which is why this symptom is suspected of COVID-19.

Can you taste without smelling?

The scent of freshly ground coffee, fresh bread, rolls or cookies at Christmas time awakens feelings and memories in everyone and makes “your mouth water”. But the sense of smell is even more closely linked to the sense of taste, as most people who have eaten their favourite foods while suffering from a stuffy nose and found that they suddenly taste different should know.

Food and drink taste bland with just the tongue, and eating is no fun if you can’t smell it. Therefore, the sense of taste and smell must work together so that a harmonious whole emerges.

Relationship between smell and taste

The sense of smell (the technical term is olfactory perception) and the sense of taste (gustatory perception in technical jargon) are chemical senses: The invisible molecules of the starting materials reach the olfactory mucosa via the mouth and nose.

Salty, sweet, sour, bitter, umami (savoury, meaty, spicy) – only the tongue recognizes these five flavours using its taste buds. From there, special cell networks, so-called receptors, forward the perceived taste to the brain via various cranial nerves.

With the help of the nose, on the other hand, one can distinguish thousands of smells. The olfactory cells, also called “olfactory sensory cells”, are activated by smells. Almost all of these nerve cells are located in a small area on the roof of the central nasal cavity, in the olfactory epithelium. Millions of olfactory cells are located here. The signals are sent directly to the brain via the olfactory nerve.

In the brain, the information passed on by the sensory cells is linked, which means that aromas can then be recognized and assigned.

The trigeminal nerve,  the sensory nerve, plays a vital role in the interaction of smell and taste: This cranial nerve, which splits into three branches that extend to the eye, upper and lower jaw, conveys sensations such as the burning of chilli or the cooling effect from menthol.

Disorders of taste and smell

Taste and smell can be affected independently or both together by various disorders:

• Medicine calls it “hyposmia” when the sense of smell is partially lost.
• “Anosmia” is the technical term for destroying the sense of smell.
• One speaks of parasomy when odours are misperceived (odours are usually perceived as unpleasant).
• A taste disorder or taste disorder is referred to as dysgeusia.
• A complete loss of the sense of taste is called ageusia.
• If taste impressions are misperceived, one speaks of parageusia.

 

Lost sense of smell: These are possible causes.

If the sense of smell is gone, there can be various reasons. A common cause of temporary loss of smell is, in most cases, a cold with a runny nose. Here, swelling of the nasal mucosa leads to impairment of the sense of smell. Influenza viruses also colonize the mucous membranes and can temporarily disturb the epithelium of the olfactory mucosa. Nasal polyps or a sinus infection also impair the sense of smell. Sensory perceptions return after the illness has subsided.

The sense of smell can also be restricted in smokers and people who, for example, work extensively with strong-smelling chemicals. In rare cases, an olfactory disorder is also congenital.

Olfactory disorders in Alzheimer’s and Parkinson’s disease

In addition, there can also be central olfactory disorders in the brain, for example, diabetes, high blood pressure, malnutrition or malnutrition. Some medications can also disturb the sense of smell and taste. Studies have shown that around 80 per cent of all Parkinson’s and Alzheimer’s patients have olfactory disorders at an early stage. The causes of the odour disorders in both diseases are not in the disturbed olfactory sensory cells but directly in the brain.

From around the age of 65, the ability of the olfactory cells to regenerate decreases. The perception of taste also regresses, albeit not as strongly. As a result, many older people sometimes over-spice their food and prefer sweets. From the age of 80, 80 per cent of the population suffers from disorders of the sense of smell and taste.

Lost sense of taste: possible reasons

A loss of the sense of taste can also have harmless causes, such as a cold. In addition, taste disorders in ​​the taste buds can also be caused by iron or vitamin B12 deficiency, kidney or liver diseases or as a side effect of certain medications.

In addition, damage to the brain or cranial nerves, for example, due to tonsillectomy, ear surgery, encephalitis or diseases such as multiple sclerosis and Parkinson’s, can be responsible for a lost sense of taste.

 

Corona: COVID-19 is the cause of the disruptions

Possible symptoms of infection with SARS-CoV-2 include a disturbance or even loss of the sense of smell and taste. While the exact causes have not yet been clarified, it is becoming apparent that the disorders are usually temporary. However, there are significant differences in the duration.

• The taste buds, made up of skin cells, need about two weeks to regenerate after damage, so the sense of taste is back in many sufferers quite quickly after the disease has subsided.
• On the other hand, the loss of the sense of smell can last for several months. In the case of an infection with the coronavirus, the smell disturbance does not occur as with a cold due to a swollen nose but due to damage to the sensory cells of the olfactory system. In this case, the sensory cells are not skin but nerve cells (neurons). It can take several months for these to be renewed.

Diagnosis: That’s what the doctor does

To discover the cause of the disease, the doctor examines the nose, the nasal mucous membranes and the nasopharynx. He then checks the sense of smell on both sides and does a taste test. A nasal patency check and allergy test are also required to rule out an allergy. If necessary, the paranasal sinuses are examined using X-rays or computed tomography.

If there is a suspicion of a coronavirus infection, the doctor will arrange a test for COVID-19.

If the symptoms cannot be explained in this way, the doctor checks whether the cause lies in the brain.

What can you do if you no longer have a sense of smell?

If you lose your sense of smell or taste, it is always important to find out the cause first. The first step is always to go to the doctor so that he can carry out the appropriate examinations. Depending on the diagnosis, he can then select the appropriate treatment. The focus is always on treating the underlying disease. This can be done with medication or dietary supplements, for example, or it can also require an operation.