Loss of Taste and Smell: Causes Besides Covid

Loss of taste and smell most often comes from something blocking or inflaming the nose: a respiratory virus, chronic rhinitis, sinus disease or a nasal polyp. Head injury, aging, some medications and neurologic disease account for much of the rest. Covid belongs on the list, but it has moved a long way down it since 2020.

What is actually causing it, statistically

StatPearls divides smell loss into two mechanisms:

• Conductive, meaning a mechanical blockage that prevents odor molecules from reaching the olfactory nerves — nasal polyps, mucus, swelling.
• Sensorineural, meaning damage anywhere along the nerve pathway from the nose to the brain.

Inflammatory and obstructive disease accounts for 50 to 70 percent of cases, chiefly chronic rhinitis and sinus disease. Head trauma is the next frequent cause. NIDCD adds aging, sinus infections, smoking, nasal growths, hormonal changes, dental problems, chemical exposure, medications, radiation therapy and neurologic disease including Parkinson’s and Alzheimer’s.

NIDCD estimates that 1 to 2 percent of North Americans report a problem with their sense of smell, though that figure climbs steeply with age.

Why taste disappears with smell

Because most of “taste” is not taste. StatPearls puts smell at 95 to 99 percent of chemosensation, with the tongue responsible for the remaining sliver — sweet, salty, sour, bitter and umami. Retronasal olfaction, the odor traveling up from the back of the throat while you chew, supplies nearly everything else people call flavor. That is why someone whose problem is entirely nasal reports that food “has no taste.”

Covid: a much weaker signal than it was

In 2020, sudden smell loss was close to diagnostic. That is no longer true, and the change is measured, not anecdotal.

A psychophysical case-control study across four waves found olfactory dysfunction in 80.6% of D614G-era infections, 83.0% with alpha and 65.6% with delta, but 36.3% with omicron. A larger systematic review and meta-analysis by von Bartheld and Wang, covering 62 studies and 626,035 omicron patients, estimated global prevalence at about 3.7%, rising to 11.7% in people of European ancestry and falling between 1.9% and 4.9% in other groups — a two- to tenfold reduction against earlier variants, compared with roughly 43% in pre-omicron meta-analyses.

Two practical consequences:

• Not losing your smell tells you almost nothing about whether you have covid. Test instead — see covid symptoms and mild covid symptoms.
• Losing it is not proof of covid either. Every other respiratory virus, and chronic sinus disease, can do the same thing, and always could.

Parosmia: when smell returns wrong

Parosmia is a distorted perception of an odor that is actually present — coffee smelling like garbage, meat smelling like chemicals. NIDCD lists it alongside hyposmia (reduced smell), anosmia (no smell) and phantosmia (smelling something that is not there). It commonly appears during recovery from post-viral loss rather than at the start, as regenerating olfactory neurons wire back imperfectly, and it is distressing enough that people often describe it as worse than the anosmia it replaced.

Smell and age

Smell fades with age far more than most people expect. StatPearls cites NHANES data showing measured smell impairment in about 4% of adults aged 40 to 49, rising to 39% of those over 80, with 14 to 22% of people over 60 affected. NIDCD reports smell problems in nearly 25% of men aged 60 to 69 against roughly 11% of women in the same bracket. Gradual, painless loss over years in an older adult is a different clinical story from a sudden loss over 48 hours.

What helps

• Treat the underlying cause. Where the problem is inflammatory or obstructive, intranasal glucocorticoids or surgery for chronic sinus disease address the actual blockage.
• Smell training, for post-viral loss. The standard protocol uses four odors from distinct chemical classes — rose, eucalyptus, lemon and clove are the classic set, though household items such as coffee or cinnamon work — inhaled for about 15 seconds each, twice daily. Two randomized trials in post-viral olfactory loss found better outcomes with training than with control, and one reported improvement in 63% of a high-concentration training group against 19% of controls. It is a months-long commitment, usually a minimum of six.
• Time, realistically. Recovery is slow and partial for many: 40 to 60 percent see some spontaneous improvement over the years following diagnosis.
• Kitchen safety while it lasts. Without smell you cannot detect a gas leak, smoke, or food that has spoiled. Working detectors and dated leftovers stop being optional.

When to see an ENT

Book an evaluation with an otolaryngologist if the loss has lasted more than two to three weeks after an infection cleared, if it followed a head injury, if it came on suddenly with no respiratory illness at all, if it is one-sided, if it arrives with headache or neurologic symptoms, or if parosmia is persistent and interfering with eating. Formal smell testing exists and gives a baseline worth having.

This content is informational and does not replace a medical consultation, diagnosis, or treatment.