Anosmia, the complete inability to smell odors, contrasts with hyposmia, which involves a partial loss of the sense of smell. Individuals with anosmia may still recognize basic tastes like salty, sweet, sour, and bitter, but may struggle to discern specific flavors. Surprisingly, the ability to distinguish flavors primarily relies on smell rather than taste receptors on the tongue. Consequently, those experiencing a loss of smell often report a diminished sense of taste and reduced enjoyment of food.

Age-related changes, such as a decline in smell receptors, contribute to decreased olfactory ability in older individuals. Typically, individuals notice alterations in smell perception around age 60, with more significant changes occurring after age 70.

Causes of anosmia vary and can include conditions where nasal passages are inflamed or obstructed, preventing odors from reaching the olfactory area, or damage to parts of the olfactory system or the nerves connecting it to the brain. Common causes encompass:

Head injuries, particularly in younger adults Viral infections Alzheimer’s disease, predominantly in the elderly Head trauma often leads to permanent loss of smell, such as in vehicular accidents. Such injuries can harm or sever olfactory nerve fibers, which transmit signals from olfactory receptors to the brain. Infections or tumors near the nasal cavity’s cribriform plate, which separates the nasal and brain cavities, can also damage olfactory nerves.

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.