Post-COVID-19 Olfactory Disorders: Diagnosis, Prognosis, and Treatment Strategies

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1. Introduction

The pandemic caused by Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) has had profound repercussions on healthcare systems worldwide, initially characterized by acute respiratory symptoms. However, as scientific knowledge has evolved, it has been observed that COVID-19 presents a broad clinical spectrum, including persistent neurological, sensory, and systemic manifestations, even after the resolution of the acute phase of the infection. Among these changes, olfactory dysfunction has emerged as one of the most characteristic signs of the disease, frequently reported since the early months of the pandemic (BUTOWT; VON BARTHELD, 2021) [7, 43].

COVID-19-related olfactory changes include anosmia, hyposmia, parosmia, and phantosmia, which may occur in isolation or in association with taste changes. Epidemiological studies have demonstrated a high prevalence of these symptoms during the acute phase of infection, varying according to the viral variant, the diagnostic method used, and the population characteristics evaluated. Recent meta-analyses estimate that millions of individuals worldwide have experienced some degree of COVID-19-related olfactory impairment (SANIASIAYA; ISLAM; ABDULLAH, 2021) [41, 6].

Although most patients experience spontaneous recovery in the first few weeks after infection, a significant proportion goes on to develop persistent olfactory dysfunction. Longitudinal studies have shown that symptoms can persist for months or even years after the initial episode, constituting an important component of post-COVID syndrome or Long COVID. This persistence has sparked growing scientific interest due to its functional, psychological, and social impact (HU et al., 2023; DIAS et al., 2024) [21, 13]. The pathophysiological mechanisms responsible for COVID-19- associated olfactory loss are not yet fully understood. Evidence suggests that SARS-CoV-2 does not act primarily by directly destroying olfactory neurons, but rather by compromising the sustentacular cells of the olfactory epithelium, triggering inflammatory processes, cellular alterations, and structural changes that affect the neural transmission of odorous stimuli (BUTOWT; VON BARTHELD, 2021; ZAZHYTSKA et al., 2022) [7, 51]. In addition to peripheral changes, neuroimaging studies have demonstrated structural and functional alterations involving the olfactory bulb, orbitofrontal cortex, and other brain areas related to olfactory processing. Recent findings have identified volumetric reduction of the olfactory bulb and persistent cerebral metabolic changes in patients with prolonged olfactory loss, suggesting the involvement of central mechanisms in the maintenance of symptoms (PETERSEN et al., 2024; GUEDJ et al., 2025) [36, 17]. The diagnosis of post-COVID olfactory changes represents a significant clinical challenge. Although many patients subjectively report changes in their sense of smell, studies demonstrate significant discrepancies between self-perception of symptoms and results obtained through objective assessment methods. Thus, standardized psychophysical tests have become essential tools for identifying and quantifying olfactory dysfunction (HANNUM et al., 2021; LE BON et al., 2022) [19, 26]. Among the most widely used diagnostic instruments are the University of Pennsylvania Smell Identification Test (UPSIT), the Sniffin’ Sticks Test, and other internationally validated psychophysical scales. These tools allow for the assessment of olfactory thresholds, odor discrimination, and odor identification ability, providing objective data for clinical monitoring and evaluation of therapeutic response (HUMMEL et al., 2023; EO et al., 2024) [22, 15]. The prognostic assessment of patients with post-COVID olfactory dysfunction has also received increasing attention in the literature. Longitudinal studies suggest that factors such as advanced age, greater initial severity of olfactory loss, the presence of parosmia, and prolonged persistence of symptoms may be associated with poorer rates of functional recovery (LECHIEN et al., 2022; ZHOU et al., 2025) [27, 52]. Parosmia, characterized by a distorted perception of odors, has frequently been observed during the olfactory recovery process. Although it may indicate neural regeneration in certain cases, its presence is associated with significant impairment of quality of life, impacting patients’ nutrition, social interaction, and mental health (SCHAMBECK et al., 2021; GUENDER et al., 2024) [42, 18].

The psychosocial repercussions of persistent olfactory changes are well documented. The loss of the ability to detect odors directly interferes with food perception, environmental safety, and social interaction, contributing to symptoms of anxiety, depression, and reduced quality of life. These effects become even more relevant in individuals with symptoms persisting for long periods (OTTE et al., 2023; OLESZKIEWICZ et al., 2025) [33, 32].

In recent years, several therapeutic strategies have been proposed for the treatment of post-COVID olfactory dysfunction. Among them, olfactory training has established itself as the intervention with the highest level of scientific evidence, based on repetitive and systematic exposure to different odor stimuli with the aim of stimulating neuroplasticity and promoting functional recovery (FORNAZIERI et al., 2021; HWANG et al., 2023) [16, 23]. Recent meta-analyses demonstrate that olfactory training promotes significant improvement in olfactory function in patients with persistent dysfunction, especially when initiated early and maintained over prolonged periods. Furthermore, studies suggest additional benefits regarding the subjective perception of symptoms and quality of life (ASSERI et al., 2025; CHEN et al., 2025) [1, 11].

In parallel, pharmacological therapies are being investigated as potential complementary strategies. Topical corticosteroids, systemic corticosteroids, intranasal vitamin A, essential fatty acids, and anti-inflammatory agents have been evaluated in various studies, although results remain heterogeneous and, in many cases, inconclusive (KIM et al., 2022; WANG et al., 2023) [24, 45].

More recently, emerging therapies involving palmitoylethanolamide combined with luteolin (PEA-LUT), platelet-rich plasma (PRP), and other regenerative approaches have begun to be studied as promising alternatives for patients refractory to conventional treatments. Preliminary results suggest potential therapeutic benefit, although controlled studies with greater methodological robustness are still needed (CAPRA et al., 2023; CAPRA et al., 2025) [9, 8].

Given the high prevalence of post-COVID olfactory disorders, their significant impact on quality of life, and the growing body of scientific literature on diagnostic methods and therapeutic strategies, it is essential to critically synthesize the available evidence. In this context, the present systematic review aims to analyze recent advances related to the diagnosis, prognosis, and treatment of post-COVID-19 olfactory disorders, contributing to the updating of scientific knowledge and the improvement of evidence-based clinical practice

2. Objectives

2.1. General Objective

To analyze, through a systematic review of the literature, the main scientific evidence related to post-COVID-19 olfactory changes, with a focus on diagnostic methods, prognostic factors, and therapeutic strategies currently available for the management of persistent olfactory dysfunction.

2.2. Specific Objectives

• To identify the main pathophysiological mechanisms involved in the development of olfactory changes associated with SARS-CoV-2 infection. • To assess the prevalence of different post-COVID-19 olfactory manifestations, including anosmia, hyposmia, parosmia, and phantosmia. • To describe the subjective and objective diagnostic methods used in the assessment of olfactory function in patients with post-COVID syndrome. • Analyze the clinical applicability of standardized psychophysical tests used in the investigation of olfactory dysfunction. • To investigate the factors associated with spontaneous recovery or prolonged persistence of olfactory changes following SARS-CoV-2 infection. • To evaluate the main prognostic factors related to functional recovery of the sense of smell. • To examine the impacts of persistent olfactory changes on patients’ quality of life, mental health, diet, and social interaction. • Analyze the efficacy of olfactory training as a therapeutic strategy for the recovery of olfactory function. • To evaluate the scientific evidence related to the use of pharmacological therapies, including topical and systemic corticosteroids, vitamin A, anti-inflammatory agents, and adjuvant therapies. • Investigate the outcomes of emerging therapies, such as palmitoylethanolamide combined with luteolin (PEA-LUT), platelet-rich plasma (PRP), and regenerative approaches. • Compare the benefits and limitations of the different therapeutic strategies currently available. • To synthesize the most recent scientific evidence on the diagnosis, prognosis, and treatment of post-COVID-19 olfactory disorders, contributing to the improvement of evidence-based clinical practice.

3. Methodology

3.1. Study Design

This study consisted of a systematic literature review, conducted in accordance with the recommendations of the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA 2020), aiming to identify, select, critically evaluate, and synthesize scientific evidence related to post-COVID-19 olfactory changes, covering diagnostic, prognostic, and therapeutic aspects.

3.2. Search Strategy and Information Sources

The literature search was conducted in the PubMed/MEDLINE, Scopus, Web of Science, Embase, and Cochrane Library databases, as they are internationally recognized as important sources of biomedical and scientific literature.

The search strategy was developed using Medical Subject Headings (MeSH) terms and free-text terms related to the topic, combined using the Boolean operators AND and OR. The following strategy was used as a basis: ("COVID-19" OR "SARS-CoV-2") AND ("Olfactory Dysfunction" OR Anosmia OR Hyposmia OR Parosmia OR Phantosmia) AND ("Diagnosis" OR Prognosis OR Treatment OR Therapy OR "Olfactory Training").

3.3. Search Period

Studies published between January 2021 and June 2026 were included, a period corresponding to the consolidation of scientific evidence on olfactory changes associated with COVID-19 and their therapeutic approaches.

3.4. Inclusion Criteria

The following were included: • Original studies, systematic reviews, meta-analyses, and clinical trials; • Publications in English; • Studies involving patients with COVID-19-associated olfactory changes; • Studies addressing the diagnosis, prognosis, or treatment of post-COVID olfactory dysfunction; • Articles available in full; • Studies published between 2021 and 2026.

3.5. Exclusion Criteria

The following were excluded: • Studies duplicated across databases; • Isolated case reports, editorials, letters to the editor, and expert opinions; • Studies conducted exclusively in animal models; • Studies without a clearly described methodology; • Articles that did not specifically address olfactory changes related to COVID-19; • Studies without relevant data for extraction.

3.6. Study Selection Process

Initially, all identified records were exported for bibliographic management. After removing duplicates, the titles and abstracts were independently evaluated by two reviewers.

Potentially eligible articles were read in full to confirm inclusion criteria. Disagreements were resolved by consensus among the reviewers.

3.7. Data Extraction

The following information was extracted from the included studies: • Author and year of publication; • Country of origin; • Methodological design; • Number of participants; • Type of olfactory impairment investigated; • Diagnostic methods used; • Prognostic factors evaluated; • Therapeutic strategies employed; • Main clinical outcomes.

3.8. Assessment of Methodological Quality

The methodological quality of the studies was assessed using specific tools according to the design of each study. Randomized clinical trials were analyzed using the Risk of Bias 2 (RoB 2) tool, systematic reviews using the AMSTAR 2 instrument, and observational studies using the Newcastle-Ottawa Scale (NOS).

3.9. Data Synthesis

The results were organized and synthesized in a descriptive and qualitative manner, grouping the studies into three main categories: • Diagnosis of post-COVID-19 olfactory changes; • Prognostic factors related to olfactory recovery; • Pharmacological and non-pharmacological therapeutic strategies.

3.10. PRISMA Flowchart

The process of identifying, screening, assessing eligibility, and including studies will be presented using a flowchart developed in accordance with the PRISMA 2020 guidelines, ensuring transparency, reproducibility, and methodological rigor in the selection of articles included in this systematic review.

Figure 1 presents the PRISMA flowchart regarding the process of identification, screening, eligibility, and inclusion of the studies selected for this systematic review. The search strategy conducted in the major biomedical databases initially yielded 612 potentially relevant records. After removing duplicates, the remaining studies underwent evaluation of titles and abstracts, followed by a full reading of the potentially eligible articles. At the end of the selection process, 60 studies met all established methodological criteria and were included in the qualitative synthesis of this review.

Fig 1 The selection process revealed a high initial volume of publications related to olfactory changes associated with COVID-19, reflecting the growing scientific interest in the topic since the onset of the pandemic. However, most of the studies were excluded because they did not specifically address the diagnostic, prognostic, or therapeutic aspects of post-COVID olfactory dysfunction. The rigorous application of eligibility criteria allowed for the selection of studies with greater methodological and clinical relevance, ensuring a comprehensive and up-to-date analysis of the available evidence. The 60 included articles encompass different methodological designs and provide important information on the pathophysiological mechanisms, diagnostic methods, prognostic factors, and therapeutic strategies currently used in the management of persistent olfactory changes associated with SARS-CoV-2.

4. Results

Table 1 presents a summary of the main studies included in this systematic review, highlighting the methodological design, thematic focus, and key findings related to post-COVID-19 olfactory changes. The selected studies cover different aspects of the condition, including pathophysiological mechanisms, diagnostic methods, prognostic factors, and therapeutic strategies, allowing for a comprehensive analysis of the most recent scientific evidence.

Table 1: Summary of the main studies included in the systematic review Author/Year Study Type Main Topic Key Findings Tong et al. (2021) Systematic Review and Meta-analysis Prevalence High prevalence of olfactory changes during COVID-19 infection Butowt and Von Bartheld (2021) Review Pathophysiology Cellular mechanisms involved in SARS-CoV-2-induced anosmia Hannum et al. (2021) Observational Study Diagnosis Objective tests identify a higher prevalence than subjective reports Le Bon et al. (2022) Clinical Study Diagnosis Importance of standardized psychophysical assessment Kim et al. (2022) Systematic Review Pharmacological Therapy Corticosteroids show variable results O'Byrne et al. (2022) Cochrane Review Treatment Evidence remains limited for various therapies Park et al. (2022) Translational Review Long COVID Mechanisms of persistent loss of smell Hu et al. (2023) Meta-analysis Prognosis Persistence of dysfunction in a significant proportion of patients Hwang et al. (2023) Systematic Review Olfactory training Significant benefits in functional recovery Asvapoositkul et al.

(2023) Systematic Review Treatment Olfactory training yields better overall results Petersen et al. (2024) Neuroimaging Study Prognosis Reduction in olfactory bulb volume associated with persistent symptoms Ayoub et al. (2024) Observational Study Long COVID Association between olfactory dysfunction and dysautonomia Eo et al. (2024) Comparative Study Diagnosis Differences between classic post-viral dysfunction and post-COVID dysfunction Zaid et al. (2024) Prospective Study Prognosis Assessment of olfactory recovery rates Chen et al. (2025) Meta-analysis Treatment Multidimensional benefits of olfactory training Bischoff et al. (2025) Review Emerging therapies New therapeutic options under investigation Horwitz et al. (2025) Multicenter Cohort Long COVID Significant persistence of olfactory dysfunction Saccardo et al. (2025) Longitudinal Follow-up Prognosis Symptoms persisting for up to four years Zarkadi et al. (2026) Systematic Review Prognosis Current evidence on the persistence of olfactory dysfunction Piqueras-Sánchez et al.

(2026) Molecular Study Pathophysiology Identification of new biomarkers associated with recovery Table 2 presents the main methods used in the diagnostic evaluation of post-COVID-19 olfactory changes, ranging from simple clinical tools to objective tests and neuroimaging methods. The organization of the methods makes it clear that the diagnosis of persistent olfactory dysfunction should combine subjective assessment, standardized psychophysical tests, and, in selected cases, complementary anatomical or functional investigation.

Table 2: Main diagnostic methods used in the evaluation of post-COVID-19 olfactory changes Diagnostic method Purpose of the evaluation Main clinical applications Advantages Limitations Targeted clinical history Identify the onset, duration, intensity, and type of olfactory disturbance Initial screening for anosmia, hyposmia, parosmia, and phantosmia Simple, quick, and low-cost Subjective and dependent on the patient’s perception Subjective olfactory scales Quantify self-perception of olfactory loss Monitoring of clinical progression and therapeutic response Easy to administer in an outpatient setting May underestimate or overestimate actual dysfunction Sniffin’ Sticks test Assess odor threshold, discrimination, and identification Objective diagnosis and follow-up Standardized and widely used Requires specific materials and training UPSIT Assess odor identification Diagnostic confirmation and severity classification Internationally validated May be subject to cultural and linguistic influences Simplified olfactory identification tests Quickly assess the ability to recognize odors Use in clinical screening and population studies Practical and lower cost Less detailed assessment of olfactory function Associated gustatory assessment Distinguish between olfactory loss and true gustatory- y impairment Investigation of combined complaints of smell and taste Assists in differential diagnosis Not always available in clinical practice Nasal endoscopy Evaluate nasal obstructive or inflammatory causes Exclusion of rhinosinusitis, polyps, and anatomical obstructions Allows for direct anatomical evaluation Does not quantify olfactory function Magnetic resonance imaging Investigate the olfactory bulb and central pathways Persistent, atypical, or refractory cases Evaluates central structural abnormalities High cost and not routinely indicated Functional neuroimaging Assess brain metabolism and activity Research and complex cases of Long COVID Contributes to pathophysiological understanding Limited clinical availability Longitudinal follow-up Assess recovery or persistence of symptoms Prognostic definition and therapeutic adjustment Allows monitoring of treatment response Requires time and patient adherence Table 3 presents the main therapeutic strategies currently being investigated for the treatment of post-COVID-19 olfactory disorders, highlighting their mechanisms of action, level of scientific evidence, clinical benefits, and limitations. Recent literature demonstrates that, despite the significant increase in research on this topic, there is still no universally effective therapy for all patients, making it necessary to adopt individualized approaches based on the severity and duration of symptoms.

Table 3: Main therapeutic strategies for post-COVID-19 olfactory disorders and associated clinical evidence Therapeutic strategy Mechanism of action Scientific evidence Main benefits Limitations Olfactory training Stimulates neuroplasticity and regeneration of the olfactory pathways Strong evidence from systematic reviews and meta-analys Improved identification, discrimination, and perception of odors Requires long-term adherence and results may vary Intranasal topical corticosteroids Reduction of local inflammation of the olfactory epithelium Moderate evidence and heterogeneous results Possible acceleration of recovery in selected cases Inconsistent benefits across studies Systemic corticosteroids Control of persistent inflammatory processes Limited evidence Potential improvement in specific patients Increased risk of systemic adverse effects Palmitoylethanolamide + Luteolin (PEA-LUT)

Anti-inflammatory and neuroprotective action Promising evidence in recent studies Improved olfactory recovery and reduced neural inflammation Need for robust multicenter studies Platelet-Rich Plasma (PRP) Tissue and neural regenerative stimulation Emerging evidence Potential recovery in refractory cases Few controlled studies available Intranasal Vitamin A Stimulation of neuroepithelial regeneration Preliminary evidence Possible functional recovery of the olfactory epithelium Lack of therapeutic consensus Antioxidant supplementation Reduction of neural oxidative stress Limited evidence Potential adjuvant benefit Results still inconclusive Nasal irrigation with saline solution Cleaning and improvement of the nasal environment Supporting evidence Low cost and easy application Limited standalone benefit Combination therapies Association between olfactory training and pharmacological treatment Growing evidence Possible synergistic effect on olfactory recovery Protocols not yet standardized Multidisciplinary follow-up Integrated otolaryngological, neurological, and psychological approach Recommended in persistent cases Overall improvement in quality of life and treatment adherence Need for greater availability of care The studies reviewed demonstrate that olfactory training remains the intervention with the strongest scientific support and is considered the first-line treatment for patients with persistent olfactory dysfunction. At the same time, pharmacological therapies such as topical corticosteroids, intranasal vitamin A, and neuroprotective compounds are being investigated as complementary alternatives. Among emerging approaches, the combination of palmitoylethanolamide and luteolin (PEA-LUT) and platelet-rich plasma show promising results, especially in individuals refractory to conventional therapies. Furthermore, the combination of different therapeutic modalities has demonstrated potential for optimizing functional recovery of the sense of smell. Taken together, the findings reinforce that the management of post-COVID-19 olfactory changes should multidisciplinary, progressive, and based on the most recent available scientific evidence.

Figure 2 presents the distribution of the main topics addressed in the studies included in this systematic review on post-COVID-19 olfactory changes. It is observed that most publications focused on the evaluation of therapeutic strategies, especially olfactory training and emerging pharmacological therapies. In addition, a significant portion of the studies investigated prognostic aspects related to the recovery of smell, while other studies explored diagnostic methods, pathophysiological mechanisms, and impacts on quality of life. This distribution highlights the growing scientific interest in comprehensively understanding post-COVID olfactory dysfunction and in the search for effective therapeutic approaches.

Distribution of topics in the included studies Figure 2 Caption. Percentage distribution of the main topics addressed in the studies included in the systematic review on post-COVID-19 olfactory changes. There is a predominance of research focused on therapeutic strategies, followed by prognostic, diagnostic, and pathophysiological studies. Topics related to Long COVID, dysautonomia, and quality of life also contributed to the overall understanding of persistent olfactory dysfunction.

5. Discussion

The large number of studies identified in this review highlights the growing scientific interest in understanding the pathophysiological mechanisms involved in post-COVID loss of smell. Unlike other respiratory viral infections, SARS-CoV-2 appears to primarily compromise the sustentacular cells of the olfactory epithelium, triggering inflammatory processes and microenvironmental changes capable of impairing neuronal function without necessarily causing direct destruction of olfactory neurons (BUTOWT; VON BARTHELD, 2021; ZAZHYTSKA et al., 2022) [7, 51]. In addition to peripheral changes, recent evidence suggests significant involvement of central mechanisms. Neuroimaging studies have identified a reduction in the volume of the olfactory bulb, cerebral metabolic changes, and impairment of cortical regions involved in sensory processing, such as the orbitofrontal cortex, reinforcing the hypothesis that the persistence of olfactory dysfunction may result from structural and functional changes in the central nervous system (PETERSEN et al., 2024; GUEDJ et al., 2025) [36, 17].

In the diagnostic field, the results confirm the importance of using objective methods to assess olfactory function. Comparative studies have demonstrated that patients’ self-perception often does not correspond to the actual severity of the dysfunction identified by standardized psychophysical tests, such as the University of Pennsylvania Smell Identification Test (UPSIT) and the Sniffin’ Sticks Test (HANNUM et al., 2021; LE BON et al., 2022) [19, 26]. Thus, the combination of clinical evaluation and objective tests allows for greater diagnostic accuracy and better monitoring of clinical progression.

Regarding prognosis, it has been observed that recovery of olfactory function exhibits heterogeneous patterns. Although many patients partially or fully recover their sense of smell in the first few weeks after infection, a significant proportion maintains persistent symptoms for months or even years, constituting an important component of Long COVID (HU et al., 2023; HORWITZ et al., 2025) [21, 20]. Longitudinal studies indicate that factors such as advanced age, greater initial severity of olfactory loss, and prolonged persistence of symptoms are associated with poorer rates of functional recovery (LECHIEN et al., 2022; ZHOU et al., 2025) [27, 52]. Parosmia has emerged as one of the key prognostic findings observed in the literature. Although some authors suggest that its presence may indicate ongoing neural regeneration, this alteration is frequently associated with significant impairments in patients’ eating habits, social relationships, and psychological well-being (SCHAMBECK et al., 2021; GUENDER et al., 2024) [42, 18]. These results reinforce the need for a multidisciplinary approach for individuals with persistent olfactory dysfunction.

The psychosocial repercussions identified in this review corroborate studies demonstrating an association between prolonged olfactory loss and reduced quality of life. The inability to perceive odors compromises environmental safety, interferes with food perception, and may contribute to the development of anxiety, depression, and social isolation (OTTE et al., 2023; OLESZKIEWICZ et al., 2025) [33, 32]. Consequently, quality-of-life assessment should be routinely incorporated into the follow-up of these patients. In the therapeutic setting, olfactory training has emerged as the strategy with the highest level of scientific evidence. Recent systematic reviews and meta-analyses have demonstrated significant improvement in the identification, discrimination, and perception of odors in patients undergoing structured olfactory rehabilitation protocols (FORNAZIERI et al., 2021; HWANG et al., 2023) [16, 23]. Similar results were observed by Asvapoositkul et al. (2023) [2] and Chen et al. (2025) [11], who reported consistent benefits in functional recovery and quality of life. In contrast, pharmacological therapies yielded more heterogeneous results. Topical and systemic corticosteroids, intranasal vitamin A, and antioxidant agents demonstrated potential benefit in some studies, but without definitive consensus regarding clinical efficacy or the standardization of therapeutic protocols (KIM et al., 2022; WANG et al., 2023) [24, 45]. This variability reinforces the need for randomized clinical trials with greater methodological robustness.

Emerging therapies are also attracting growing interest. The combination of palmitoylethanolamide and luteolin (PEA-LUT) has demonstrated anti-inflammatory and neuroprotective properties that may be beneficial for olfactory recovery, while platelet-rich plasma (PRP) shows promising results in patients refractory to conventional approaches (CAPRA et al., 2023; CAPRA et al., 2025) [9, 8]. However, the scarcity of multicenter trials limits their routine incorporation into clinical practice.

Overall, the findings of this review demonstrate that post-COVID-19 olfactory dysfunction remains a significant clinical and scientific challenge. Although significant advances have been made in understanding the pathophysiological mechanisms and available therapeutic strategies, important gaps still exist regarding prognostic prediction and the development of treatments capable of promoting faster and more consistent functional recovery. The results show a predominance of studies focused on therapeutic strategies, accounting for approximately one-third of the scientific output analyzed. This finding reflects the need to identify effective interventions for patients with persistent olfactory dysfunction following SARS-CoV-2 infection. Prognostic studies also accounted for a significant proportion, highlighting the interest in understanding the factors associated with spontaneous recovery or the persistence of symptoms. To a lesser extent, studies focused on pathophysiological mechanisms, quality of life, neuroimaging, and dysautonomia were identified—areas that are expanding our understanding of the systemic impacts of COVID-19. Taken together, the findings demonstrate that the current literature is directed not only toward characterizing olfactory loss but also toward developing diagnostic and therapeutic strategies capable of improving clinical outcomes for affected patients.

6. Conclusion

Post-COVID-19 olfactory changes constitute an important manifestation of the post-acute syndrome of SARS-CoV-2 infection, presenting high prevalence and potential impact on patients’ quality of life, mental health, nutrition, and social interaction. The findings of this systematic review demonstrate that the pathophysiology of olfactory dysfunction involves complex mechanisms, including peripheral alterations of the olfactory epithelium and possible central impairments of neural pathways related to sensory processing.

The results highlight that the use of objective diagnostic methods, especially standardized psychophysical tests, represents an essential tool for the proper identification and monitoring of olfactory loss. Furthermore, e y prognostic factors such as age, initial symptom severity, and the presence of parosmia can aid in predicting functional recovery and in individualized therapeutic planning. Among the available therapeutic strategies, olfactory training remains the intervention with the strongest scientific support and should be considered the primary approach for patients with persistent olfactory dysfunction. Pharmacological therapies and emerging approaches, such as PEA-LUT and PRP, show potential benefit but still require more robust evidence for broad clinical recommendation. It is therefore concluded that the management of post-COVID-19 olfactory changes should be multidisciplinary, evidence-based, and tailored to the individual characteristics of each patient. New prospective studies and controlled clinical trials are essential to improve our understanding of the mechanisms involved and to establish increasingly effective diagnostic and therapeutic protocols for this condition, which remains a significant clinical challenge in the post-pandemic period.