I don't often think about my sense of smell, unless I'm given a fragrant flower or walk past someone smoking. But the ability to smell is both critical and underappreciated, according to Zara Patel, MD, a Stanford assistant professor of otolaryngology, head and neck surgery.
A smell begins when a molecule -- say, from a flower -- stimulates the olfactory nerve cells found high up in the nose. These nerve cells then send information to the brain, where the specific smell is identified. Anything that interferes with these processes, such as nasal congestion or damage to the nerve cells, can lead to a loss of smell.
I recently spoke with Patel about the loss of the sense of smell, a condition known as anosmia.
How does losing the sense of smell impact patients?
If asked which sense they'd give up first, most people would likely choose their sense of smell. It's only after the loss of olfaction that its significant impact on our lives is appreciated. Our sense of smell plays a key role in a vast array of basic human interactions, such as what attracts us to sexual partners, what keeps us in committed relationships and how maternal bonding occurs with newborns. It's also one of our most basic protective mechanisms that allows us to wake up in the midst of a fire and prevents us from eating spoiled food. And importantly -- keeping in mind that our ability to taste is highly dependent on our ability to smell -- the inability to enjoy food and related social activities often causes social isolation, depression and malnutrition.
What causes olfactory loss?
There are over 100 reasons why people can lose their sense of smell. However, the majority of people lose it from sinonasal inflammatory disease, post-viral infections, traumas or tumors. Unfortunately, olfactory loss is often of idiopathic origin, meaning we just don't know what caused it. That is why research in this area is so important.
It's also important to be treated as early as possible. It is always frustrating to see someone who lost their sense of smell over a year ago, but they weren't referred to me at the time or were told that nothing could be done. Those are missed opportunities that will negatively impact those patients for the rest of their lives.
How do you treat patients who can no longer smell?
The treatment really depends on the reason for loss, and may include surgery or medications. For those who lose the ability to smell after trauma, post-viral infection or when we don't know why it happened, olfactory training can be used, which is a very simple protocol that patients can do at home. The patients smell several essentials oils in a structured way twice a day, every day, over a long period of time. The oils -- rose, eucalyptus, clove and lemon -- stimulate different types of olfactory receptor cells in the nose. Although it does not help everyone, it has been shown to be effective in 30 to 50 percent of patients.
We don't have an exact understanding of how and why it works. However, a study using functional MRI observed a change in how the brain responds to odors before and after olfactory training. Before the training, there was a chaotic array of random areas lighting up in the brain. After the training, the images showed a renewed pathway to the olfaction center in the brain. We also know that the olfactory nerve has an inherent ability to regenerate. We're trying to take advantage of this fact and switch on those regenerative cells.
I have many patients who have benefited from olfactory training, including some who need their sense of smell for their livelihood -- such as chefs or wilderness guides. Being able to get that sense back has allowed them to continue doing what they're passionate about and has increased their quality of life.
What are you working on now?
Although olfactory training has allowed us to help more patients, 30 to 50 percent improvement is still quite low and certainly not the final answer. That's why the research I'm currently doing has me excited about the potential of using both stem cells and neurostimulation to advance this field. I hope to soon be able to offer alternative interventions to these patients.