Effects of a 4-week combined breathing control and self-talk intervention on neural activity and coping skills in athletes: a randomized control trial.

Chemosensory dysfunction (CSD), defined as impairment in smell, taste, flavor, or chemesthesis, is common in upper respiratory infections, including COVID-19, as well as chronic sinonasal diseases such as chronic rhinosinusitis (CRS). Normal chemosensory perception depends on smell (olfaction), taste (sweet, salty, sour, bitter, umami), flavor (retronasal smell), and chemesthesis (sensations like cooling, burning, warming, or tingling) . When these systems are disrupted, people may develop a variety of sensory disturbances, including: anosmia (loss of smell), ageusia (loss of taste), hyposmia (reduced smell), hypogeusia (reduced taste), parosmia (distorted smell), dysgeusia (distorted taste), phantosmia (perceiving a smell when no odor is present), phantogeusia (perceiving a taste when no tastant is present), or loss of chemestheic sensations, such as the burn from spicy foods or the tingle from carbonated beverages . Persistent COVID-19–related CSD is a recognized chronic condition within the post-acute sequelae of COVID-19 . The abrupt and profound loss of smell and taste was a distinguishing symptom of acute COVID-19 infections in the first pandemic waves . Although less severe and widespread, CSD is still a persistent manifestation even with newer strains of COVID-19 in the US . About 4% of people recovering from COVID-19 report long-lasting CSD worldwide with about 4 million in the U.S. alone . This form of CSD is marked by disruption of taste , distorted flavor perception , phantosmias, and parosmias . Importantly, current topical and systemic anti-inflammatory therapies have largely been ineffective for persistent COVID-19 CSD, and there are currently no therapies that consistently work to improve the persistent olfactory and gustatory dysfunction resulting from COVID-19 . Some of these features are known to distinguish this syndrome from the pre-COVID-19 viral and chronic inflammatory nasal syndromes . CRS, specifically CRS with nasal polyps (CRSwNP), is another major cause of chemosensory loss . Up to 90% of patients with CRSwNP experience hyposmia or anosmia . A severe CRSwNP subtype, aspirin-exacerbated respiratory disease (AERD), affects about 0.9% of the population and causes intense sinonasal inflammation. In CRSwNP and AERD, olfactory loss significantly affects quality of life, causing safety concerns, social isolation, and reduced well-being, but unlike COVID-19 CSD, smell often improves with corticosteroids or biologics such as dupilumab . Despite their differences, the full spectrum of chemosensory experiences, including the shared and unique features of COVID-19 CSD and AERD CSD, have not been fully defined or explored, preventing further insights into CSD as a condition.