What are smell disorders and what causes them? (2023)

What are smell disorders? What are the causes of bad breath (distortion inthe sense of smell) and why do they appear? Why is this so important?

The sense of smell and the importance of our sense of smell

It would be hard to imagine life without experiencing the scent of a rose or the taste of morning coffee. Smell, our sense of smell, plays an important role in almost everyone's life.

Our sense of smell not only helps us detect aromas in the air around us, but it is also important in helping us enjoy the taste of food. You may have heard that "taste" is mostly smell, and that's pretty much true. A damaged sense of smell is seriously disturbing: the pleasure of eating and drinking can be lost and depression can result. In addition, there are risks associated with itloss of smell, including the inability to detect gas leaks or spoiled food.

More than 2.7 million people in the United States have an olfactory disorder, and that is likely an underestimate. Some people have suggested that about half of people over the age of 60 have a reduced sense of smell.

Anatomy and physiology of smell (the sense of smell)

In the upper and middle part of the nose there is a small cellular area called the olfactory mucosa. This area secretes several protective substances, such as immunoglobulins (antibodies that bind to foreign bodies such as microorganisms), to prevent pathogens from entering the head. There are also a large number of proteins, called receptors, that bind chemicals in the environment, or odorants. Each container is believed to have a special shape that fits these aromatics, like a key fits a lock.

Olfactory receptors reside in approximately six to ten million olfactory chemoreceptors in each nasal cavity. New receptors are formed in adulthood - one of the few examples of how the brain can form new nerve cells throughout life. When there is a match between an environmental chemical and a receptor on an olfactory cell, the nerve cell sends a signal directly to the brain at the olfactory bulb.

While the olfactory bulb is usually considered the “firstcranial nerve,” technically not a nerve, but part of the brain itself. The signals transmitted by the olfactory bulb travel to special parts of the cerebral cortex and even to the amygdala, which is a part of the brain involved in emotions. From the primary olfactory cortex, signals are transmitted to other parts of the brain, including the thalamus and hypothalamus.

Smell disorders

There are several terms used to describe the different types of smell disorders. These include:

• dysomia:Distortion of smell. Dysodor, on the other hand, is divided into two different types of smell disorders.Parosmasrefers to a change in the perception of an odor. Phantom, on the other hand, refers to the perception of an odor that is not there. With halitosis, the odor may also smell different than it used to smell to you, or you may now find a repulsive odor that you used to enjoy. With phantasm, for example, you can smell a fire when there is no fire.
• Aftertaste:Reduced sense of smell
• Anosmia:Complete inability to smell odors

Causes of dysomia (a distortion in the sense of smell)

There are various factors and conditions that can cause bad breath.

The most common causes are diseases of the nose and sinuses: by clogging the nasal passages and inflaming the tissue that receives odor molecules, viral infections and allergies have an effect on our sense of smell that almost everyone has experienced at some point. Conditions related to the nose, such asnasal polyps, deviated septum, as well as surgery and trauma to the nose (such as rhinoplasty) can disrupt the sense of smell.

Other possible causes include:

• Head injury:Traumatic brain injury can affect smell in several different ways: The nose can be damaged, or the nerve fibers that send information from the nose to the brain can be cut or torn during the head injury. Trauma can also directly damage the olfactory bulb that detects the molecules we smell.
• Brain tumors:Bothmalignant and benign brain tumors, especially those involving the olfactory bulb or temporal lobes, may be associated with a change in the sense of smell. In some cases, loss of smell can be the first symptom of a malignant or benign brain tumor.
• Toxins in the environment:Tobacco products and smoke reduce the sense of smell. Toxins such as ammonia, sulfuric acid and formaldehyde can also reduce the sense of smell.
• Medicines:Some drugs, especially some classes of drugs used to control high blood pressure, can affect the sense of smell. Examples include Procardia (nifedipine), Vasotec (enalapril), and Norvasc (amlodipine).
• Head and neck radiation for cancer
• Neurological disorders:More than 90 percent of people with Alzheimer's disease have problems smelling, and bad breath is also commonParkinson's disease.
• Diabetes:Similar to the nerve damage that can lead to peripheral neuropathy and retinopathy in diabetes, damage to the nerves involved in smell can also occur.
• Vitamin deficiency:Zinc deficiency or thiamine deficiency leads toWernicke-Korsakoff syndromassociated with loss of smell.
• Sjøgren's syndrome: This autoimmune condition can lead to partial or total loss of smell.

The sense of smell generally decreases both with natural aging and with degenerative diseases such as dementia. While the mature olfactory bulb in young adults has approximately 60,000 mitral neurons, both the number of mitral neurons and the diameter of their nuclei decrease dramatically with age.

In about one in five people with smell disorders, the cause is "idiopathic," meaning there is no specific cause.

Diagnosis of smell disorders

Diagnosis of olfactory disorders often begins with a careful history and physical examination. A physical exam can look for signs of a viral infection or nasal polyps. A careful history may reveal potential toxic exposures.

A test known as the University of Pennsylvania Odor Recognition Test can be performed to assess whetherhyperlugtor anosmia is actually present. Since there are many possible causes ranging from brain disorders to nutritional causes and more, further investigation will depend on many factors.

Treatment and management of loss of smell

There are no specific treatments that can reverse a change in the sense of smell. Sometimes dysomy goes away on its own with time. Researchers have evaluated the use of high-dose vitamin A and zinc supplements, but so far it does not appear to be effective. Olfactory training is currently being evaluated and appears promising in early studies.

Coping is therefore the primary goal of the treatment. For those without a sense of smell, safety precautions like making sure you have a fire alarm are important. Nutritional counseling may be helpful as certain foods and spices are more likely to stimulate the receptors (trigeminal and olfactory chemoreceptors).

Bottom line on the sense of smell and disorders that affect our sense of smell

The importance of smell and taste is generally underestimated in everyday society. Whilelugtnervecalled cranial nerve number one, indicating the importance of smells, in practice the sense of smell is rarely tested (even by neurologists). While it is true that the human olfactory system is relatively small compared to other mammals, the sense of smell helps us both. enjoy life and protect ourselves from environmental toxins.

WithPeter Pressman, MD
Peter Pressman, MD, is a board-certified neurologist developing new ways to diagnose and care for people with neurocognitive disorders.