Loss of taste: I can't taste my food. What is causing it?

The flavour of what we eat is a combination of two senses. The taste buds on the tongue detect only the basic tastes: sweet, salty, sour, bitter and umami (the savoury taste in foods such as stock and cheese). As we chew, the smell of the food rises from the back of the mouth into the nose, and the brain combines the two into the flavour we call strawberry, coffee or mint. MSD Manuals notes that recognising complex flavours, such as raspberry, requires both the sense of taste and the sense of smell.

That is why the commonest real cause of a taste complaint lies in the nose. The US National Institute on Deafness and Other Communication Disorders (NIDCD) states that most people who think they have a taste disorder actually have a problem with smell. The NHS lists among the common causes of lost smell illnesses such as a cold, flu and COVID-19, sinusitis (a sinus infection), allergies such as hay fever and polyps in the nose; it adds some medicines and, rarely, more serious conditions such as Parkinson's disease or epilepsy.

There is a simple way to tell the two apart at home. Pinch your nostrils firmly shut with your fingers, put a sweet with a distinct flavour or a slice of fruit in your mouth and chew. With your nose closed you only get a sense of sweet or sour and cannot say which fruit it is; this is normal. Keep chewing and let go of your nose. If the flavour suddenly arrives, both your tongue and your nose are working. If nothing changes when you let go but you can still taste the sweetness and sourness, the problem is most likely on the smell side; if you cannot tell sweet, salty and sour apart either, true loss of taste is considered. This test does not make a diagnosis; it points you to the right doctor: for a smell problem, an ear, nose and throat specialist; for a taste problem, first the dentist or your GP.

With true loss of taste, the first place to look is saliva. Taste substances dissolve in saliva to reach the taste buds; when the mouth dries out, taste weakens too. MSD Manuals lists among the causes of a dry mouth that reduces taste Sjögren's syndrome, heavy smoking and especially pipe smoking, radiotherapy to the head and neck, and dehydration; it adds zinc, copper and nickel deficiency. The same source notes that a burn on the tongue temporarily damages the taste buds, and that depression and seizure disorders can also affect taste.

Medicines are the second large group. MSD Manuals lists among the medicines that can change taste antibiotics, anti-seizure medicines, antidepressants, chemotherapy drugs, diuretics, medicines for rheumatism and thyroid medicines. NIDCD states that if a medicine is the cause, stopping or changing it can resolve the problem. Do not make that decision yourself: tell the doctor who prescribed the medicine whether the change in taste came after you started it, and they will make any change needed. According to the NHS, the chlorhexidine mouthwash your dentist gives you can also cause a brief burning or tingling feeling or an unusual taste in the mouth; this eases as you keep using it.

Nerves are the third group. Taste from the front two thirds of the tongue is carried by a fine branch that leaves the facial nerve (the chorda tympani); this branch joins the lingual nerve just below the base of the skull, and the lingual nerve in turn runs in the mouth along the inner side of the lower jaw, right next to the wisdom tooth. MSD Manuals writes that Bell's palsy, a paralysis of the facial nerve, disturbs taste on the front two thirds of one side of the tongue. The NHS, too, lists loss of taste among the symptoms of Bell's palsy, alongside weakness on one side of the face, a drooping eyelid, drooling and a dry mouth. This is why loss of taste on one side matters so much: it may be pointing to the facial nerve on the same side.

People often wonder about wisdom tooth removal and taste. NIDCD lists the removal of a third molar (wisdom tooth) among the causes of taste disorders. But the measured data show that the problem is rare. In Barcelona, the tongues of 16 patients who had a lower wisdom tooth removed were tested before the extraction, and one week and one month afterwards: a slight reduction in the sense of touch was found at one week and had fully recovered at one month, while no change at all was found in the ability to taste. In a review that screened 27 studies, the rate of permanent lingual nerve damage stayed on average between 0.07% and 0.28%, depending on the surgical technique used; temporary effects were more common. If numbness and loss of taste started together on one half of your tongue after an extraction, report it to the clinician who did the extraction the same week.

There is a separate situation for denture wearers: the palate. An upper full denture covers the whole palate with pink acrylic, and there are taste receptors on the palate too. In a study of 170 upper denture wearers in Brazil, a taste test was repeated with the denture in the mouth and with it removed; with the denture in, taste perception fell significantly, and recognising bitter taste became hardest, followed by salty, sweet and sour. In Amsterdam, 21 patients used upper dentures held by two implants first with a palate and then with the palate cut away; their satisfaction with taste rose markedly once the palate was opened. If food has tasted different since a new upper denture, the cause is most likely this covering.

The pictures in the first list mostly recover once the cause goes away. If even a single item from the second list applies to you, stop watching and waiting.

The order starts from danger: first a stroke and the facial nerve are ruled out, then smell is separated from taste, and last of all the mouth and teeth are examined.

1. 1

   First, a check of the face and speech

   Look in the mirror and smile, raise both arms in front of you and hold them for a few seconds, and say a simple sentence. If your mouth or eye drops to one side, an arm drifts down or your speech is garbled, the assessment is made in A&E; call 112.

2. 2

   Smell or taste: the two are separated

   The food test with the nose closed and open can be done at home. At the doctor's, sweet, sour, salty and bitter solutions are used; MSD Manuals writes that taste can be tested with sugar, lemon juice, salt and bitter substances.

3. 3

   Each side of the tongue is tested separately

   The taste substance is applied to the right and left front parts of the tongue separately. A reduction on one side only suggests the facial nerve or the lingual nerve on that side. NIDCD states that an ear, nose and throat specialist can establish how severe the loss is by measuring the lowest concentration that can be detected.

4. 4

   You are asked about your medicines and procedures

   Medicines started in recent months, mouthwashes you use, wisdom tooth removal, an implant or middle ear surgery, radiotherapy to the head and neck, and head injury are gone through one by one. NIDCD lists ear and nose surgery and wisdom tooth removal among the causes of taste disorders.

5. 5

   The mouth and teeth are examined

   The amount of saliva, a coating or thrush on the surface of the tongue, gum inflammation, decay and how much of the palate the denture covers are assessed. NIDCD also lists poor oral hygiene and dental problems among the causes of taste disorders.

6. 6

   Blood tests and referral if needed

   If a nutritional problem, kidney disease or diabetes is suspected, your GP requests tests. For a smell problem, ear, nose and throat comes in; where a nerve is involved, neurology.

There is no single treatment for loss of taste; what is done depends on where the loss comes from.

The following are wrong steps often seen with this complaint. We set them out so that, whichever doctor you see, you can ask the right questions.

The time depends on the cause. The sequence below is a general framework; the plan of the clinician who examines you takes priority.

1. The weeks after an infection

   Loss of smell and flavour linked to a cold or flu usually gets better as the nose clears. The NHS writes that it can get better within a few weeks or months.

2. If a few weeks have passed

   The NHS advises seeing a GP if your sense of smell has not returned to normal within a few weeks. This is the point at which to stop waiting at home.

3. The first month after wisdom tooth removal

   In the Barcelona study, the slight loss of touch on the tongue was found at one week and had fully recovered at one month. Numbness or loss of taste lasting beyond a month should be shown again to the clinician who did the procedure.

4. Months with Bell's palsy

   The NHS writes that symptoms should get better within 6 months, and that for some people it can take longer.

We do not give a single figure here, because behind a loss of taste there may be a cold that passes on its own, a side effect that calls for a change of medicine, or a denture that needs replacing. On the dental side, these are the items that determine the scope:

The source of the loss

Loss of taste from smell, a medicine, a nerve or the mouth takes entirely different routes and falls to different doctors.

Treatment needed in the mouth

If there is gum inflammation, decay or thrush, treating them goes into the plan as separate items.

The type of denture

Adjusting a denture that covers the palate and an implant-supported solution that leaves the palate open are not the same scope.

Tests and imaging

Taste tests, blood tests and, where needed, a nerve assessment may call for separate appointments.