Losing your sense of smell, whether partially or completely, is a relatively common problem that affects an estimated 3 to 20% of the population. A complete loss is called anosmia, while a reduced ability to smell is called hyposmia. The causes range from something as simple as a stuffy nose to something that needs medical attention, so understanding the context of your smell loss matters.
The Most Common Causes
The single most frequent reason people lose their sense of smell is an upper respiratory infection, including colds, sinus infections, and flu. The virus inflames the tissue inside your nose that detects odors, temporarily blocking or damaging it. For most people, smell returns once the infection clears.
Beyond infections, the National Institute on Deafness and Other Communication Disorders lists these common causes:
- Nasal blockages: polyps or other growths in the nasal cavity physically prevent odor molecules from reaching the smell receptors
- Head injury: a blow to the head can sever or damage the delicate nerve fibers that connect your nose to your brain
- Aging: smell naturally declines over time, particularly after age 60
- Smoking: chronic exposure damages the tissue lining the nose
- Medications: some antibiotics, antihistamines, and other drugs can interfere with smell
- Chemical exposure: insecticides, solvents, and other harsh chemicals can injure the smell receptors
- Hormonal changes: shifts in hormones can temporarily alter your sense of smell
- Dental problems: infections or procedures involving the upper teeth, which sit close to the nasal sinuses, can affect smell
COVID-19 and Smell Loss
COVID-19 brought smell loss into widespread awareness. The virus can damage the cells that support the smell receptors in the nose, leading to sudden and sometimes total loss. The good news: most people recover. In one study published in Scientific Reports, patients reported their smell dysfunction lasted an average of about 1.3 months, with a range from two weeks to 14 months. Only a small number reported persistent changes after their acute illness resolved.
If you lost your smell during or after a COVID infection and it hasn’t returned after several weeks, smell training (covered below) is the most studied intervention for speeding recovery.
How Your Nose Heals Itself
Your sense of smell has something unusual going for it: the nerve cells responsible for detecting odors are one of the few types of neurons in your body that regenerate throughout your life. Deep in the tissue lining your nose, stem cells called basal cells sit in reserve. When smell receptors are damaged, these stem cells activate, divide, and mature into new odor-detecting neurons. The new neurons then grow connections back toward the brain’s smell-processing center.
This regeneration cycle takes roughly 30 to 90 days per neuron. It’s why many cases of smell loss resolve on their own, though severe damage to the tissue or to the brain structures involved can slow or prevent full recovery.
When Smell Loss Signals Something Neurological
A declining sense of smell can sometimes be an early sign of a neurodegenerative condition, particularly Parkinson’s disease or Alzheimer’s disease. In Parkinson’s, smell impairment often appears years before the more recognizable motor symptoms like tremor or stiffness. Researchers now consider olfactory loss one of the earliest detectable markers of both conditions.
The connection makes biological sense. Odor information travels from the nose through the olfactory bulb to brain regions involved in memory, recognition, and cognition, including the hippocampus and prefrontal cortex. These are the same areas affected early in Alzheimer’s and Parkinson’s. That said, most people who lose their sense of smell do not have a neurodegenerative disease. This link is most relevant if smell loss is gradual, unexplained by other causes, and accompanied by other subtle changes like memory difficulties or movement issues.
How Smell Loss Affects Eating and Weight
Smell and taste are deeply intertwined. Much of what you perceive as “flavor” is actually smell, which is why food can taste flat or unrecognizable when your nose isn’t working. This has real consequences for nutrition and body weight, though not always in the direction you’d expect.
Some people eat less because food loses its appeal. Others eat more, chasing flavor satisfaction they can’t quite reach. Research on people with post-COVID smell loss found that many gravitated toward foods high in sugar and salt because those flavors registered more strongly. After one year, people with ongoing smell dysfunction showed statistically significant increases in body mass index. The pattern makes sense: when you can’t smell your food, you tend to compensate with intensity rather than variety.
Safety Risks You Should Know About
Your sense of smell acts as an early warning system, and losing it creates real safety gaps. A study in JAMA Otolaryngology broke down the hazardous events reported by people with impaired smell: cooking-related incidents accounted for 45%, eating spoiled food made up 25%, failing to detect a gas leak represented 23%, and being unable to smell a fire accounted for 7%.
If your smell loss lasts more than a few weeks, take some practical steps. Install smoke detectors and natural gas detectors on every floor of your home, and check them regularly. Date all perishable foods when you buy them, and ask someone in your household to periodically check the fridge for anything that’s gone off. If you cook with gas, consider switching to electric or at minimum ensuring your gas appliances are regularly inspected.
Smell Training: The Primary Recovery Tool
Smell training is the most evidence-backed approach for recovering lost smell. The standard protocol involves sniffing four distinct scents twice a day for at least 12 weeks. The classic set is rose, lemon, eucalyptus, and clove, chosen because they each represent a different odor category.
A randomized clinical trial found that about 38% of people who did smell training experienced a clinically meaningful improvement, compared to 24% in a control group who did no training. The best results came from a combined approach: participants who chose scents they personally recognized and paired the sniffing with looking at images of the scent source saw improvement rates of 53%. So picking scents that are familiar and meaningful to you, and actively visualizing them while sniffing, appears to help. Popular patient-chosen scents included lemon, lavender, eucalyptus, vanilla, and sandalwood.
The training works by stimulating the regeneration process in your nasal tissue, essentially giving those new neurons repeated signals to wire themselves correctly. It requires patience and consistency, but it’s something you can do at home with essential oils or the actual source materials.
How Doctors Test Your Smell
If you see a doctor about smell loss, they’ll likely start by examining the inside of your nose with a scope to look for polyps, swelling, or structural issues. Formal smell testing uses standardized scratch-and-sniff kits. The most common is the University of Pennsylvania Smell Identification Test, a 40-question multiple-choice test where you scratch a scented strip and try to identify the odor. Scores below certain thresholds confirm hyposmia or anosmia. Another widely used tool, Sniffin’ Sticks, uses pen-like devices held under the nose and scores identification on a 16-point scale.
Symptoms That Need Prompt Attention
Most smell loss resolves on its own or has an obvious cause like a cold. But certain accompanying symptoms suggest something more serious. Seek evaluation promptly if your smell loss comes with bleeding from only one side of the nose, crusting or scabbing inside the nasal cavity, swelling around the eyes or visual changes, severe frontal headaches, swelling of the forehead, or any new neurological symptoms like confusion, weakness, or neck stiffness. These combinations can point to structural problems, infections, or growths that require imaging or specialist referral.