Problems with smell and taste can have a big impact on our lives. These senses contribute to our enjoyment of life by stimulating a desire to eat, which nourishes our bodies and enhances our social activities. When smell and taste become impaired, we eat poorly, socialize less and feel worse. Smell and taste also warn us of potential dangers such as fire, toxic fumes, and rotten food. Loss of the sense of smell may indicate sinus disease, growths in the nasal passages, or, in rare cases, brain tumors.
Most patients who complain of a loss of taste suffer from a loss of smell. The majority of a food’s flavor comes from our ability to smell it. The tongue can only sense salt, sweet, sour, bitter, and umami (or savory). Because of this, a cold or stuffy nose can make it difficult to taste food.
True disorders of only taste are rare. Disorders of smell and taste, on the other hand, affect approximately 2 million people in the United States.
The complicated process of smelling and tasting begins when molecules released by substances around us stimulate special nerve cells in the nose, mouth, or throat. These cells transmit messages to the brain, where specific smells or tastes are identified.
Olfactory (smell nerve) cells are stimulated by the odors around us such as the fragrance of a flower or the smell of brewing coffee. These nerve cells are found in a small patch of olfactory mucosa (tissue) high up in the nose and connect directly to the brain.
Gustatory (taste nerve) cells are clustered in the taste buds of the mouth and throat. They react to food or drink mixed with saliva. Many of the small bumps on the tongue contain taste buds. These surface cells send taste information to nearby nerve fibers, which send messages to the brain.
Our body’s ability to sense chemicals also contributes to our senses of smell and taste. Thousands of free nerve endings—especially those on the moist surfaces of the eyes, nose, mouth, and throat—identify sensations like the sting of ammonia, the coolness of menthol, and the heat of hot peppers.
Loss of smell can result from a physical blockage of the nose or damage to the olfactory cleft or nerve. Patients with a deviated septum or allergies may have nasal obstruction, which prevents odors from reaching the olfactory cleft. Nasal polyps, which occur in patients with chronic sinusitis, can block smells from entering the nose. Very rarely, loss of smell can come from benign or malignant tumors in the nose.
Inflammation and swelling from chronic sinusitis can also cause loss of smell. It can damage smell permanently by injuring the olfactory mucosa.
The common cold or viral upper respiratory infection often causes inflammation in the nose, which can impair smell. Ordinarily, this loss of smell returns days to weeks after the initial illness. However, a small number of patients experience a more prolonged or permanent loss of smell. Many patients without a clear reason for their loss of smell and taste likely have viral-related loss of smell but do not remember the illness.
Zinc nasal sprays used to prevent or shorten flu or colds have been found to cause sudden, permanent smell loss. Patients with this type of loss describe an immediate burning sensation when using the spray followed by loss of smell. The over-the-counter nasal spray Zicam, for example, caused this sensation in people, which led to its removal from stores. This spray is no longer available and should not be used under any circumstances.
Trauma to the head such as in a car accident can cause injury to the brain or the olfactory nerves, leading to temporary or permanent smell loss. The sense of smell also diminishes with age in a similar fashion as vision and hearing.
The physician examining a patient for loss of smell will need to examine the inside of the nose. This usually involves performing a nasal endoscopy. The physician will look for conditions that can block the nose such as a deviated septum, nasal polyps or inflammation. The physician may also use a scratch-and-sniff or other test to determine the severity of smelling loss.
If there is not an obvious reason for the loss of smell, a physician may order an MRI to check for any abnormalities in the olfactory cleft, olfactory nerve, and brain.
If allergies or other inflammatory diseases have caused a patient’s loss of smell, a physician may recommend nasal or oral steroids to decrease the inflammation. Surgery may be recommended if the patient has nasal polyps, chronic sinusitis, a deviated septum or other surgically treatable disorders.
Unfortunately, patients with a permanent loss of smell after a viral illness or without a clear reason for their loss of smell have limited treatment options. A short course of oral steroids may help some patients. Research is ongoing to determine the cause and potential treatment for this type of smell loss.