Anosmia is related to multiple factors
1.Conditions that cause temporary irritation or congestion inside your nose may include:
Acute sinusitis,Chronic sinusitis,Common cold,
COVID-19,allergic rhinitis,Influenza (flu),Nonallergic rhinitis,Smoking
Obstructions of your nasal passages
2. Nasal obstruction :
Deviated nasal septum,Nasal polyps,Tumors
3. Olfactory nerve damage(Nerves leading to the area of the brain that detects smell or the brain itself can be damaged or deteriorate due to)
Aging,Alzheimer's disease,Brain aneurysm,Brain surgery,Brain tumor,
Diabetes
Exposure to chemicals in certain insecticides or solvents
Next Steps
Thorough history, investigation