Though many people take it for granted, the ability to smell provides many useful purposes. Odors can act as warning signs for fires, gas leaks, spoiled food, and the presence of chemicals in the air. Additionally, smells add variation to how food tastes. Individuals with anosmia completely lack a sense of smell. Though anosmia is not usually a sign of a serious condition, it can be problematic in everyday life. It can also potentially lead to weight loss, malnutrition, and depression.
To understand how anosmia occurs, it is helpful to understand how the body’s sense of smell works. The process of smelling begins when the nose inhales small molecules floating in the air. These molecules then attach to receptors in the nose’s mucous membranes, which stimulate nerves that connect to the brain. Issues impacting any steps in this process can lead to partial or complete loss of smell. Minor causes may resolve with time, while serious issues may not be treatable.
Some conditions cause irritation or congestion that affects the mucous membranes inside the nose. Upper respiratory infections are the most common cause of anosmia. Sinus infections, particularly acute sinusitis, can cause excess mucus to form in the sinuses. This can block the openings of the sinuses and lead to anosmia. The common cold and influenza are also common triggers of temporary anosmia. A less common condition that can lead to anosmia is nonallergic rhinitis. The symptoms are similar to hay fever or allergic rhinitis but lack the evidence of an allergic reaction. Nonallergic rhinitis typically features a chronic stuffy or runny nose, which can prevent a person from smelling properly.
Beyond irritation or congestion, physical obstructions can develop in the nose and block the flow of air. Some people are born with congenital bone deformities that impair their sense of smell. They may also be prone to chronic sinusitis, which may cause anosmia. Individuals may develop teardrop- or grape-shaped growths along their nasal passages or sinuses. These nasal polyps are typically soft, painless, and benign. However, if they grow too large, they can block airflow.
Some of the more dangerous conditions that cause anosmia result from or cause brain and nerve damage. Any trauma that damages the olfactory nerve or olfactory system in the brain can potentially cause anosmia. Some degenerative conditions such as Parkinson’s disease and Alzheimer’s occasionally feature anosmia as an early symptom. Many other conditions and diseases can cause a person to lose their sense of smell. In addition, certain medications and nasal sprays can damage the pathways that enable smell.
Sometimes, a person loses only their ability to smell certain odors, a condition referred to as specific anosmia. Though many physicians believe that specific anosmia is a rare condition, a recent study indicated otherwise. Unlike general anosmia, treatment methods for specific anosmia involve smell training over the course of several months. Frequent exposure to the odors that an individual cannot perceive may eventually cure the condition.
Though the vast majority of cases of anosmia are the result of another condition, there are rare cases of a person being born with a lifelong inability to smell -- congenital anosmia. Some people with congenital anosmia experience no other symptoms, and others have other genetic disorders. Physicians remain unable to determine the cause of congenital anosmia. Additionally, it appears as though the condition is sporadic and familial cases are uncommon. Many children with congenital anosmia pretend to be able to smell, making it difficult for parents to seek treatment.
Because they cannot smell, people with anosmia have unique difficulties that do not affect the general population. Notably, loss of smell can be dangerous because people with anosmia can’t smell gas leaks, smoke, or spoiled food. Though minor in comparison, these people also are unable to tell when they have bad breath or body odor. Individuals who experience sudden onset anosmia may find food significantly less appetizing, which can negatively affect their weight and even lead to malnutrition.
Though some physical effects of anosmia are dangerous, the mental effects can be similarly debilitating. Many people with anosmia experience depressive episodes. Other individuals may view anosmia trivial, which can negatively impact the mindsets of those with the condition. Furthermore, memories and smells link together in an interesting way. Anosmia means people either lose or cannot form sentimental smell memories such as the unique scent of a loved one, a new book, freshly cut grass, and many other scents. Losing these smell memories can lead to severe feelings of depression.
Interestingly, anosmia can be difficult for doctors to diagnose properly, mostly because testing both nostrils at the same time tends to lead to an inaccurate test result. Instead, physicians will press one nostril shut and use a pungent odor to test the other nostril. They then repeat the process with the second nostril. If a patient can properly identify the odor, the doctor can assume the patient doesn’t have anosmia. If anosmia is present, doctors may refer to medical histories to find possible underlying causes such as trauma. CT scans or MRI scans can sometimes identify previously undiagnosed conditions.
In general, anosmia has no effective treatment. Instead, healthcare professionals aim to treat specific causes in the hope that the anosmia will resolve. However, the ability to smell may not return even with successful treatment of the initial cause. Steroids have proven beneficial at improving anosmia that results from nasal inflammation. Gene therapy is very early in development but is capable of restoring a sense of smell in rats born with congenital anosmia. It is possible that gene therapy will be an effective treatment for humans with anosmia in the future.
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