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Anosmia, also known as smell blindness, is the loss of the ability to detect one or more smells. Anosmia may be temporary or permanent. It differs from hyposmia, which is a decreased sensitivity to some or all smells. Anosmia can be categorized into acquired anosmia and congenital anosmia. Acquired anosmia develops later in life due to various causes, such as upper respiratory infections, head trauma, or neurodegenerative diseases. In contrast, congenital anosmia is present from birth and is typically caused by genetic factors or developmental abnormalities of the olfactory system. While acquired anosmia may have potential treatments depending on the underlying cause, such as medications or surgery, congenital anosmia currently has no known cure, and management focuses on safety precautions and coping strategies. Anosmia can be due to a number of factors, including inflammation of the nasal mucosa, blockage of nasal passages, or destruction of temporal lobular tissue. Anosmia stemming from sinus inflammation is due to chronic mucosal changes in the lining of the paranasal sinus and in the middle and superior turbinates. When anosmia is caused by inflammatory changes in the nasal passageways, it is treated simply by reducing inflammation. It can be caused by chronic meningitis and neurosyphilis that would increase intracranial pressure over a long period of time, and, in some cases, by ciliopathy, including ciliopathy due to primary ciliary dyskinesia. The term derives from the Neo-Latin anosmia, based on Ancient Greek ἀν- (an-) + ὀσμή. Some people may be anosmic for one particular odor, a condition known as "specific anosmia". The absence of the sense of smell from birth is known as congenital anosmia. In the United States, 3% of people aged over 40 are affected by anosmia. Anosmia is a common symptom of COVID-19 and can persist as long COVID.