Taste disturbance: possible causes

Taste disorder is defined as an altered sense of taste, including decreased sensitivity, complete loss, distorted perception, or the sensation of taste without a stimulus. Clinical terms include hypogeusia as a decrease, ageusia as a loss, dysgeusia as a distortion, and phantageusia as a "phantastic" taste. It is important to distinguish taste problems from olfactory disorders, as a significant number of "taste" complaints are due to a decreased sense of smell and impaired perception of the aroma of food. A proper diagnosis begins with recognizing what is impaired: taste, smell, or a combination of both. [1]

Taste disorders occur in people of all ages, but are more common in the elderly and in patients with comorbidities or polypharmacy. Symptoms negatively impact nutrition, body weight, food enjoyment, food safety, and quality of life. Some patients experience taste distortions for only certain categories, such as a persistent metallic taste or excessive bitterness. Others experience impaired recognition of the basic taste modalities: sweet, salty, sour, bitter, and umami. [2]

The gustatory pathways involve taste receptors in the taste buds of the tongue and palate, afferent fibers of the facial, glossopharyngeal, and vagus nerves, nuclear complexes of the medulla oblongata, and higher centers. Damage can occur at any level, from local factors in the oral cavity to central structures. This explains the variety of causes, from xerostomia and candidiasis to micronutrient deficiencies, drug effects, neurodegenerative and immune conditions. [3]

In recent years, new themes have emerged: post-viral disorders, including those following coronavirus infection; drug-induced disorders in modern treatments for oncological, infectious, and cardiometabolic diseases; and the impact of aging and lifestyle factors. Therefore, the approach to the patient should be algorithmic, step-by-step eliminating reversible causes. [4]

International Classification of Diseases Code 10 and 11

In the International Classification of Diseases, Tenth Revision, taste disorders are classified under section R43 "Disorders of Olfaction and Taste." Codes such as R43.2 "Parageusia" for distorted perception and R43.8 "Other and unspecified disorders of olfaction and taste" are also possible. Clinical documents often use R43 in the absence of a more precise nosology, and in secondary forms, the code for the underlying disease is added. [5]

The International Classification of Diseases, Eleventh Revision, includes a separate code, MB41.2, for "Dysgeusia," as well as entries for other disorders of the chemical senses. This level of detail is useful for accurately describing the phenotype, planning examinations, and monitoring. National adaptations may use additional categories within the same block. [6]

Table 1. Correspondence of International Classification of Diseases codes

Classifier	Chapter	Code	Description
ICD-10	Olfactory and taste disorders	R43.2	Parageusia as a distorted taste
ICD-10	Olfactory and taste disorders	R43.8	Other and unspecified disorders of smell and taste
ICD-11	Disorders of smell or taste	MB41.2	Dysgeusia
ICD-11	Disorders of smell or taste	MB41.YZ	Other specified and unspecified violations

Source: official reference books of the International Classification of Diseases. [7]

Epidemiology

According to surveys of the adult population, taste changes are reported by approximately 17-20% of people, and the prevalence increases with age. In a sample of residents over 40 years of age, 19% reported taste disturbances, and among those over 80 years of age, 27%. This reflects the contribution of aging, polypharmacy, and comorbidities. [8]

Population studies show variations in estimates due to methods and criteria. One study using objective tests estimated the prevalence of taste disorders to be 17.3%. Other data indicate that approximately 9.8% of adults in the United States report taste disorders, which correlates with data indicating increased burden on the healthcare system. [9]

The pandemic has brought the issue into sharp focus: taste dysfunction with coronavirus infection resolves within weeks for most patients, but some report longer-lasting symptoms. Long-term, persistent taste dysfunction is less common than olfactory dysfunction, but it impacts nutrition and well-being. [10]

In hospitals and dental departments, a significant proportion of cases involve patients with oral diseases caused by candidiasis, gingivitis, periodontitis, and salivary dysfunction. This emphasizes the importance of oral examination and treatment of local causes. [11]

Table 2. Examples of prevalence estimates

Population	Prevalence assessment	Comment
Adults over 40 years of age	19%	self-reporting in primary care
Adults over 80 years of age	27%	higher due to polypharmacy and concomitant pathology
Objective taste tests	17.3%	Taste strips technique and thresholds
Population of the United States	9.8%	survey, self-report of tastes or smells

Reasons

Causes are conventionally divided into local, systemic, neurogenic, medicinal, and post-viral. Local causes include xerostomia, inflammatory diseases of the oral cavity, dental problems, and fungal infections. Systemic causes include zinc, iron, and vitamin deficiencies, endocrine and metabolic disorders, and liver and kidney disease. Neurogenic causes involve the peripheral and central structures of the taste tract. [12]

Drug-induced dysgeusia is a common and under-recognized cause. According to reviews, more than 200 drugs can cause taste changes: antibacterial agents, antihypertensive drugs, chemotherapy drugs, antihistamines, and angiotensin-converting enzyme inhibitors. Discontinuing or replacing the offending drug often results in improvement. [13]

Postviral disorders, including those following coronavirus infection, typically affect both smell and taste. Although many patients experience taste recovery within months, some patients experience distortions or "phantom" taste sensations, requiring supportive measures and observation. [14]

Disturbances in salivary flow and saliva composition play a significant role: saliva dissolves taste buds, delivers them to the taste buds, and protects the mucous membrane. Decreased salivation in autoimmune diseases and after head and neck treatments can exacerbate taste complaints. Treatment is aimed at restoring salivary function and improving oral hygiene. [15]

Table 3. Main etiological groups and first steps

Group of reasons	Examples	First steps
Local	candidiasis, gingivitis, xerostomia	Oral cavity sanitation, infection treatment, restoration of salivation
Systemic	deficiency of zinc, iron, vitamins, hypothyroidism	laboratory screening and correction of deficiencies
Medicinal	antibiotics, angiotensin-converting enzyme inhibitors, chemotherapy	revision of the regimen, replacement according to indications
Post-viral	after coronavirus infection and other viruses	observation, supportive measures, rehabilitation

Risk factors

Age is an important non-modifiable factor: with age, the number of taste buds decreases, salivation changes, and associated diseases become more common. This explains the increase in prevalence after age 40 and especially after age 80. [16]

Smoking, poor oral hygiene, and chronic inflammation increase the risk of dysgeusia. Eliminating these factors often leads to partial or complete improvement of complaints. Smoking cessation programs and dental disease prevention are important elements of management. [17]

Polypharmacy increases the risk of drug-induced taste disturbances, especially in the elderly and in patients with chronic diseases. Regular review of medication lists and deprescribing reduce the risk of taste disturbances. [18]

Micronutrient deficiencies, particularly zinc, have been associated with taste disturbances in various clinical groups, including those following bariatric surgery and chronic diseases. In these scenarios, identifying and correcting deficiencies significantly impacts outcome. [19]

Pathogenesis

Normally, taste molecules bind to receptors on taste bud cells, triggering transduction cascades and transmitting a signal along fibers of the facial, glossopharyngeal, and vagus nerves to the nucleus of the solitary tract, then to the thalamus and cortex. Any link in this chain can be disrupted. Damage to individual nerves produces "regional" defects, while central lesions lead to more complex phenotypes. [20]

Xerostomia disrupts the dissolution and delivery of taste buds to the receptors, reducing sensitivity and increasing unpleasant sensations. Salivary proteins and ions influence the thresholds for sweet, salty, sour, bitter, and umami tastes, so changes in saliva composition manifest as selective disturbances. [21]

Medicines affect taste through various mechanisms: direct chemical absorption of the drug in saliva, effects on receptor proteins, changes in salivation, neurotoxic effects, and effects on taste bud regeneration. Often, the mechanisms are combined, so the clinical presentation is polymorphic. [22]

Postviral disorders are associated with mucosal inflammation, damage to supporting cells, impaired taste bud regeneration, and interactions with the olfactory system. Spontaneous compensation is possible in some patients, but recovery time varies. [23]

Symptoms

Hypogeusia is characterized by a decreased ability to distinguish basic tastes. Patients describe food as "bland," a need to add salt and spices, and difficulty distinguishing sweet, sour, salty, bitter, and umami flavors. Ageusia is rare and usually accompanies severe damage to the taste tract. [24]

Dysgeusia is a distorted taste, the most common complaint. Characterized by a persistent metallic taste, bitterness, or a "rotten" odor, sometimes intensified by certain foods or medications. Phantageusia is the sensation of taste without a stimulus, often leading to anxiety and a decrease in quality of life. [25]

Taste complaints often coexist with olfactory ones, and then the primary problem is a decreased perception of aromas. During the interview, it's important to clarify the specific qualities lost, which helps plan tests. Correctly distinguishing between taste and olfactory disturbances changes treatment strategies. [26]

Associated symptoms suggest the cause: dry mouth in autoimmune diseases, burning tongue in candidiasis or burning mouth syndrome, numbness and pain in cranial nerve lesions, signs of deficiencies or endocrinopathy. These details guide the selection of tests and consultations. [27]

Classification, forms and stages

Clinicians divide taste disturbances into quantitative and qualitative forms. Quantitative forms include hypogeusia and ageusia, while qualitative forms include dysgeusia and phantageusia. Subtypes are described by their relationship to food intake, modality selectivity, and episode duration. This framework helps develop diagnostic and treatment algorithms. [28]

Based on their origin, taste disturbances are classified as primary and secondary, resulting from olfactory dysfunction. The second type is common and requires correction of the underlying causes of odor loss and restoration of nasal breathing. Distinguishing between the two types reduces the risk of unnecessary testing. [29]

Based on the anatomical level of damage, peripheral and central forms are distinguished. Peripheral forms involve the taste buds and branches of the facial, glossopharyngeal, and vagus nerves, while central forms involve the brainstem and cortical connections. The clinical presentation and prognosis depend on the level of damage. [30]

For practical purposes, it's appropriate to record severity using simple taste-recognition scales, such as "taste strips," and compare them with the patient's complaints. This helps assess progress while addressing underlying causes and rehabilitation. [31]

Table 4. Practical classification for a physician

Axis	Options	What changes
Type of violation	quantitative or qualitative	choice of tests and patient expectations
Source	primary or secondary to olfaction	priority for correction of nasal breathing
Level	peripheral or central	consultations and neuroimaging as indicated
Monitoring	test strips or thresholds	evaluation of the effect of treatment and rehabilitation

Complications and consequences

Taste disturbances impair appetite, leading to changes in eating behavior, deficiencies, and weight loss, especially in the elderly and cancer patients. Food becomes less appealing, increasing the risk of inadequate protein and micronutrient intake. Nutritional support and "flavor enhancers" can help partially offset this problem. [32]

Psychoemotional consequences include anxiety, depression, and social isolation. Enjoyment of food and shared meals is reduced, and quality of life is diminished. Timely psychosocial support and counseling on nutritional strategies significantly improve adaptation. [33]

Combined olfactory dysfunction reduces safety: it is more difficult to recognize smoke, gas leaks, and spoiled food. Training in compensation strategies and the use of household sensors improve life safety. [34]

In patients undergoing chemotherapy and following head and neck radiation therapy, taste disturbances increase mucositis, xerostomia, and reduce treatment adherence. Therefore, prevention, pain control, and early nutritional support are important. [35]

When to see a doctor

You should consult a doctor if taste disturbances, a persistent metallic or bitter taste, a noticeable decrease in taste perception, or a loss of taste without a stimulus persist for several weeks. Particularly concerning are sudden onset, asymmetry of sensations, and combination with neurological signs. [36]

Immediate consultation is required in cases of difficulty swallowing, rapid weight loss, signs of dehydration, or severe dry mouth, as well as if a drug-related cause is suspected with severe symptoms. A review of the medication list is not postponed. [37]

If the taste complaint is accompanied by loss or distortion of smell, nasal congestion, facial pain, or after a viral infection, it is logical to start with an assessment of nasal breathing and olfaction, since correction of these factors often improves taste perception. [38]

In case of long-term alcohol consumption, signs of deficiencies, after bariatric and other surgeries on the stomach and intestines, it is necessary to discuss a laboratory assessment of microelements and vitamins and possible correction. [39]

Diagnostics

Step 1. History and examination. The onset, connection with infection, medications, dental events, salivary flow, and concomitant diseases are clarified. An examination of the oral cavity, tongue, and gums is performed, nasal breathing is assessed, and simple taste tests are performed. Clues to the cause are often already apparent at this stage. [40]

Step 2. Basic laboratory panel. Recommended levels include zinc, ferritin, and iron, vitamins, glucose and glycated hemoglobin, thyroid-stimulating hormone and free thyroxine, and liver and kidney function. In the presence of xerostomia, salivary flow rate is assessed and autoimmune causes are excluded. [41]

Step 3. Objectification of taste. The most readily available test is one using validated taste strips with graduated concentrations of sweet, salty, sour, bitter, and umami. Electrical gustometry can be used in specialized centers; however, a systematic review questions its role as a screening method, although some modern studies note sensitivity in cases of abnormalities. [42]

Step 4. Instrumental diagnostics as indicated. Neurological signs are indicated by neuroimaging; if candidiasis is suspected, a mycological examination; if a drug-related cause is present, a trial dose reduction or replacement is recommended. Olfactory input is always assessed, and standardized odor testing is performed if necessary. [43]

Table 5. Diagnostic tests and the purpose of their use

Test	What does it show?	When needed
Taste strips with graduated concentrations	thresholds and total score by modality	primary objectification, monitoring of dynamics
Electrical density metering	thresholds of excitation of taste nerves by parts of the tongue	clarification of the level of damage in case of controversial clinical findings
Salivary secretion and oral examination	xerostomia, candidiasis, inflammation	for dryness and local complaints
Laboratory panel of deficiencies and endocrinopathies	zinc, iron, vitamins, thyroid gland, metabolism	almost everyone with long-term complaints

Differential diagnosis

It's important to distinguish true taste dysfunction from olfactory dysfunction. If "taste" returns when the nose is pinched, odor is likely the primary problem. In sensory ataxia due to neuropathy, complaints may resemble gustatory complaints, but objective taste recognition remains normal. Accurate collection of complaints and simple tests help differentiate these conditions. [44]

Dental and otolaryngological causes are considered separately: candidiasis, gingivitis, chronic sinusitis, and nasal obstruction. Treatment of these conditions often improves taste sensations without additional interventions. [45]

Neurogenic causes include damage to the facial or glossopharyngeal nerve following surgery, inflammation, or trauma, as well as central lesions. In the presence of focal neurological symptoms, consultation with a neurologist and neuroimaging are indicated. [46]

Drug-induced dysgeusia is diagnosed clinically based on a chronological relationship and a "positive test" of drug withdrawal or substitution. When multiple medications are involved, a stepwise approach with risk-benefit assessment is required. [47]

Table 6. What are the differences between the main “imitators”?

State	Signs "for"	Signs "against"
True taste dysfunction	reduced modality recognition on test strips	normal sense of smell in tests
Olfactory dysfunction	worsening when trying to recognize the aroma of food	objective taste tests are normal
Dental pathology	plaque, inflammation, xerostomia	lack of local finds
Medicinal cause	relationship with initiation of therapy, improvement upon discontinuation	lack of chronology with drugs

Treatment

Treatment begins with eliminating the underlying cause. For drug-induced dysgeusia, consideration should be given to replacing the offending medication with an alternative from the same class, reducing the dose, or changing the timing of administration. The decision is made in consultation with the attending physician, taking into account the benefits and risks. Improvement is possible within weeks of changing the regimen. [48]

Oral hygiene is essential for xerostomia and inflammation: professional cleaning, treatment of candidiasis, mucosal care, stimulation of salivation by chewing sugar-free gum, and, if necessary, medicinal saliva stimulants and saliva substitutes. This improves the delivery of taste buds to the receptors and reduces discomfort. [49]

Deficiency correction is key. For zinc deficiency, elemental zinc therapy is used in appropriate doses and for appropriate periods, under safety monitoring. Modern reviews and meta-analyses show benefits in patients with confirmed deficiency, idiopathic disorders, and chronic renal failure, although standard doses of zinc are often ineffective in oncology. [50]

Nutritional strategies include enhancing flavors with herbs, acidity, and umami, varying textures and temperatures, using plastic utensils instead of metal ones when metallic tastes occur, eating smaller meals, and supplementing with protein. These approaches reduce aversions and improve calorie intake. [51]

Gustatory rehabilitation utilizes taste recognition training with increasing concentrations, taste attention exercises, and combination with olfactory training for associated disorders. The evidence base is gradually growing, but these methods are already safe and appropriate as adjuncts. [52]

In post-viral disorders, taste recovery occurs within months for most patients, so the initial approach is observation, support, and training in nutritional strategies. If combined olfactory dysfunction persists, olfactory training and work on restoring nasal breathing are helpful. [53]

In cancer patients undergoing head and neck radiation therapy and chemotherapy, mucositis prevention, pain control, oral care, and early nutritional support are important. Non-drug strategies, including oral cryotherapy during some infusions and taste adaptations to the diet, reduce the severity of complaints. [54]

For patients with severe xerostomia associated with autoimmune diseases, salivary stimulants and saliva substitutes are discussed, as well as regular "wet" breaks when talking and eating. The goal is to increase comfort, reduce mucosal trauma, and improve flavor dissolution. [55]

The role of neuromodulation and pharmacotherapy beyond the correction of deficiencies remains limited. Some studies describe the benefits of alpha-lipoic acid and other agents for burning mouth syndromes, but these are not universal solutions for all taste disorders. Treatment is selected individually, based on phenotype. [56]

Patients with coronavirus infection are given realistic timelines. Objective data shows that taste returns to normal within one year for most patients, even if smell remains partially impaired. This helps set expectations and reduce anxiety. [57]

Table 7. Treatment: what, when, and with what evidence support

Approach	When to apply	Comment
Revision of drug therapy	suspected causative drug	cancellation or replacement according to indications
Oral cavity and saliva sanitation	xerostomia, inflammation, candidiasis	dentist, hygiene, saliva substitutes
Zinc deficiency	laboratory-confirmed deficiency	doses and timing as recommended, monitoring
Nutritional strategies and training	loss of appetite, disgust	flavor enhancers, textures, temperature
Rehabilitation training	persistent complaints	as a supplement, safe

Prevention

Maintain good oral hygiene, visit your dentist regularly, and monitor inflammation and tooth decay. If your mouth is dry, use moisturizers and stimulate saliva flow. This reduces the risk of local causes of taste disturbances. [58]

Avoid excessive polypharmacy, especially in the elderly: periodically review your medication list with your doctor. If the drug label lists dysgeusia as a possible side effect, discuss alternatives in advance. [59]

Maintain a balanced diet with adequate protein and micronutrients and monitor for deficiencies using laboratory tests. Particular attention is required after bariatric procedures and in chronic diseases. [60]

Quit smoking and limit alcohol consumption. These steps improve taste perception, oral health, and salivation, and reduce the risk of associated diseases. [61]

Table 8. Prevention levels and expected effect

Level	Measures	Effect
Individual	hygiene, smoking cessation, diet, correction of deficiencies	reducing the risk of taste disturbances
Medical	revision of drug regimens	less drug-induced dysgeusia
Dental	treatment of candidiasis, xerostomia	improving taste perception

Forecast

The prognosis depends on the cause. After viral infections, taste usually recovers more quickly than smell, and after 12 months, most patients have no objective taste dysfunction. This is a favorable outcome with supportive measures. [62]

In drug-induced dysgeusia, the prognosis is good with discontinuation or substitution of the offending drug. Recovery times vary from weeks to several months and depend on the pharmacokinetics and associated factors. [63]

In cases of xerostomia, salivary gland diseases, and after radiation therapy, taste restoration is more difficult and requires long-term maintenance therapy and rehabilitation. Improvement is possible with a comprehensive approach. [64]

If zinc deficiency is detected and corrected correctly, the prognosis is favorable, but effectiveness depends on the dose, duration, and underlying deficiency. In cancer therapy, standard doses of zinc are often ineffective. [65]

Table 9. Factors influencing outcome

Factor	Impact on prognosis
Discontinuation of the causative drug	there is a high probability of improvement
Correction of deficiencies	improved sensitivity
The presence of xerostomia	difficult recovery
Postviral origin	improvement within months
Radiation therapy to the head and neck	slow and incomplete recovery

Frequently asked questions

If the taste is "metallic," is it always the medication?
Not always. A metallic taste is characteristic of certain medications and micronutrient deficiencies, as well as dental and inflammatory problems. Diagnosis begins with an oral examination and a review of medications. [66]

Does zinc help everyone?
No. The greatest benefit is shown in cases of confirmed deficiency, idiopathic disorders, and chronic renal failure, when given in relatively high doses and for relatively long periods. Standard doses are often ineffective in cancer treatment. [67]

Should neuroimaging be performed on everyone?
No. It is considered in cases of focal neurological symptoms or a suspected central cause. In most cases, clinical examination, taste tests, and laboratory testing for reversible factors are sufficient. [68]

How can you differentiate a taste problem from an olfactory one?
If you have difficulty smelling food, but basic taste recognition is intact during tests, an olfactory problem is more likely. In true taste dysfunction, the recognition of sweet, salty, sour, bitter, and umami tastes is impaired. [69]

How long does it take to see improvement after a coronavirus infection?
It often takes weeks or months, and within 12 months, objective taste function returns to normal for most people, although smell may take longer to recover. Supportive measures and education on nutritional strategies can help people through this period. [70]