Many people with a smell disorder describe a loss of taste. Indeed, taste loss or other taste impairments can occur (see the end of this page for more information). However, in most cases, a perceived lack of “taste” is actually the result of a smell disorder. Why is that?
When we eat food or drink a beverage, our brain combines smell and taste information to create a perception of flavor. When you have a smell disorder, flavor perception is altered because a key component of flavor – smell – is missing, reduced or changed. Most of us would describe this as a difference in the taste of food. But if we were to put sugar, salt, citric acid or quinine on our tongue, we would still perceive sweetness, saltiness, sourness or bitterness.
Thus, if you notice a change in the flavor of food and drink it is generally advisable to be assessed for a smell disorder. If smell dysfunction can be excluded, then the less common taste disorders can be assessed.
Smell disorders can have a variety of causes.
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.
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 are regularly subjected to environmental damage from viruses 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. If that is the case, a partial or complete loss of smell function can occur.
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.
Smell disorders can impact the ability to detect odors or the ability to perceive them. These disorders are often grouped into one of four categories.
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.
Whether or not a smell disorder is treatable depends largely on its cause. In general, smell function that is impaired from either (1) the disruption of airflow in the nose or (2) from some neurological causes (epilepsy, tumors, etc.) can often be restored by treating the underlying cause. For example, smell loss caused by nasal polyps or damage to the structure of the nose can often be treatable by surgery, while smell loss caused by inflammation of olfactory tissues or by severe rhinosinusitis may be treatable with steroids and/or antihistamines.
Unfortunately, no validated treatments currently exist for congenital anosmia or for smell disorders that result from damage to the olfactory nerve or olfactory brain. Cutting edge treatments such as gene therapy and stem cell therapy hold promise for treating smell disorders, but more research and development is needed. Scientists and clinicians at the UF Center for Smell and Taste are actively pursuing research in these areas.
Even when treatment options are not available, there are things you can do that can lessen your risks for harm and improve your quality of life.
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).
Because the sense of smell is such a large contributor to the perception of flavor, many people with a smell disorder may confuse it with a lack of taste. However, some people may have a primary taste impairment. If a smell disorder can be ruled out, taste impairments or distortions may result from disruption of the taste (gustatory) system itself.
Types of taste disorders. The most common types of taste disorders are distorted taste (dysgeusia) and taste phantoms. Complete taste loss (ageusia) can also occur.
Causes. Taste disorders can have a variety of causes. For example, damage to the taste system can occur after surgeries that impact the taste nerves (such as to remove tumors in the head or neck) or after some dental procedures. Radiation or chemotherapy treatments can negatively impact the taste system. A number of common medications can lead to taste disturbances, including the appearance of a bitter or metallic taste.