About Smell Disorders

Cells within the nasal cavity called olfactory sensory neurons (or OSNs) detect odors and send that information through the skull into the brain. These OSNs, or the cells that support them, are regularly subjected to environmental damage from viruses (such as those associated with the flu, the common cold or COVID-19) or inhaled toxins. They can also be physically damaged, such as with certain head traumas. Normally, the nose is constantly generating replacement OSNs that are able to detect odors in the nasal cavity and make new connections to the brain to communicate odor information. However, sometimes the damage is too severe for this replacement process to occur efficiently, if at all. Damage to supporting cells can also disrupt the local environment of the OSNs, making it difficult for them to detect odors efficiently. In these cases, a partial (hyposmia) or complete (anosmia) loss of smell function can occur.

Sometimes smell function is impaired when the nasal passages are blocked and odors can’t reach the sensory cells (called olfactory sensory neurons or OSNs) that sit deep within the nasal cavity. Nasal polyps, damage to the structure of the nose, inflammation and severe sinusitis can create impediments to odors getting to where they need to go to be detected by the olfactory system.

Regions of the brain that receive olfactory information from the nose can be damaged, resulting in smell loss. These brain areas – including the olfactory bulb and olfactory cortex – can be damaged by physical trauma, neurodegenerative diseases, or tumors.

Some people are born without a sense of smell. This is known as congenital (“from birth”) anosmia. In many cases, congenital anosmia is thought to result from gene changes (“mutations”) that impact the structure or function of key parts of the olfactory system. Several genetic syndromes that affect multiple body systems (for example, Bardet-Beidel syndrome) can have a smell loss component.

While aging itself is not a cause of smell loss, the prevalence of a smell impairment does increase with age. One study found that nearly 25% of people from 53 – 97 years old have a smell impairment, and that the prevalence increased with age.

Sometimes, it is impossible to determine the cause of a smell disorder, though some potential causes (such as nasal polyps or severe sinusitis) can be eliminated.

Hyposmia is a reduced ability to detect odors. It can result from damage to the olfactory system or from blockage of nasal passages. Age-related hyposmia may result, at least in part, from a diminished capacity of the aging olfactory system to efficiently replace damaged olfactory sensory neurons (OSNs) with new OSNs. Individuals with hyposmia may experience anywhere from a subtle to a nearly complete loss of the ability to smell.

Anosmia is a complete loss of the sense of smell. It can result from damage to the olfactory system or from blockage of nasal passages.

Parosmia is the distortion of smell. In other words, the aroma that is perceived when smelling something is different than the smell “should” be. For example, someone smelling a flower may perceive the smell of burning rubber. When the perceived smell is unpleasant, this condition is sometimes called cacosmia.

Phantosmia is the perception an odor when no odor is present. Smell phantoms are often described as olfactory hallucination, or smelling something that is not there. Smell phantoms are sometimes experienced by people with neurological conditions such as epilepsy or schizophrenia.

If you have a smell disorder you may have difficulty identifying odors that warn of potential dangers such as a fire, a gas leak, or spoiled food. Simple strategies can help you to remain safe.

Make sure your home contains several smoke alarms and that their batteries are tested and changed regularly.
Purchase carbon monoxide and natural gas detectors and place them in any room that has a gas appliance (such as gas cooktop, water heater or clothes dryer) or an active fireplace. These detectors can be found in combination units that detect both carbon monoxide and natural gas. As with smoke detectors, make sure to test and change the batteries regularly.
Label your perishable foods with a purchase date, and discard any food that has exceeded its safe storage time. The federal government provides useful information about how long it is safe to keep foods that are perishable. Foodsafety.gov offers charts and smartphone apps that can help you to keep track of your refrigerator and freezer items.

Flavor and taste are not the same thing. Your brain combines odor and taste information to create your perception of flavor (temperature, texture, visual cues and even your experience with a food or drink can impact your perception of a flavor). Because smell is such an important part of flavor, people with smell disorders may find eating less pleasurable or even unpleasant because their perception of flavor is diminished or altered. In many cases, engaging your other senses can help. While these approaches are regularly used by trained chefs to add interest to their dishes, the added complexity may be particularly helpful to those with a smell disorder.

Combine different textures. If a dish has many soft elements, adding crunch can make a big difference.
Temperature influences our perception of what we eat and drink. You may find you prefer a particular beverage to be served at room temperature instead of on ice.
Many spices, along with carbonation, activate the third chemical sense: chemesthesis (conveyed by the trigeminal nerve). While distinct from smell or taste, chemesthetic sensations contribute to your perception of food flavor. Adding the mild burn of hot chiles, the coolness of mint, the tingling of oregano or the buzz of Szechuan peppercorns can create a more interesting dish.
Adding more “taste” elements – especially sweetness, saltiness and savoriness (that is, umami taste) – can increase the appeal. But don’t overdo it… too much sugar or salt isn’t healthy!
Most importantly, experiment with different foods, textures and flavors to learn (as well as what foods you don’t like or that trigger adverse responses).