Respiratory tract infections, notably influenza, are another prevalent cause, possibly accounting for up to a quarter of cases of diminished smell. Degenerative brain conditions like Alzheimer’s disease can impair olfactory nerves, resulting in smell loss.

Less common causes encompass medications, growths, nasal infections, allergies, sinus infections, and radiation therapy for cancer, which can temporarily or permanently affect smell or taste. Tobacco’s effect on smell remains uncertain.

In exceedingly rare instances, anosmia may be congenital.

Anosmia or reduced smell sensitivity can serve as an early indicator of COVID-19, a severe acute respiratory illness caused by the SARS-CoV-2 coronavirus.

Assessment of smell loss involves noting warning signs, particularly when accompanying head injuries, nervous system symptoms, or sudden onset of symptoms, warranting prompt medical evaluation.