**2.2 Pathophysiolgy of olfactory dysfunction**

Chen et al. reported that ACE2 immunohistochemical expression was 200 to 700 times greater in the sustentacular cells of the olfactory neuroepithelium than nasal or tracheal epithelia [20]. An animal study, showed increase in macrophages in the olfactory ephitelium and lamina propria after SARS-CoV-2 infection [21]. Generally, most data indicate that the main targets of SARS-CoV-2 are sustentacular cells in the olfactory epithelium [20–24].

These results show that hyposmia or anosmia is mainly caused by nasal epithelial infection and not a result of general malaise.
