Q&A Session with Dr. Zara Patel: Smell Training For Loss Of Smell
I invited Dr. Zara Patel, Associate Professor of Otolaryngology, Stanford Medicine to join me and talk about all things smell training for those who’ve lost their sense of smell due to COVID and other causes. As a leader in the field of smell health, she’s going to clarify much of the misinformation you find on the internet today.
Please note that the information provided in this article is for educational purposes only and does not substitute for professional medical advice about your individual situation, by your own doctor. Please consult a medical professional or healthcare provider if you’re seeking medical advice, diagnoses, or treatment for your smell dysfunction.
Can you please explain what smell training is exactly?
It’s a structured smelling protocol that aims to retrain your brain to smell. You can think of it the same way you would a person who had a stroke, who can’t move their arm, would go to physical therapy and work to get their arm moving again. When you can’t smell, olfactory training is the best way to retrain your brain and to get the olfactory neurons in the nose to regenerate. The training is a way to kick-start the regenerative process that’s inherent to the olfactory system, and allow it to make the correct connections back to the olfactory bulb and thereafter the correct connection back to the olfactory cortex - that’s what we’re trying to do with this structured smelling protocol.
How does smell training work?
You train with 4 different scents, usually essential oils. The classic scents that have been used in most scientific studies are rose, lemon, eucalyptus, and clove. The reason we choose these different scents is that they’re in different categories of smell, which means they stimulate different types of olfactory receptor neurons in the nose. They wake back up and hopefully kick-start that regenerative process that they should have.
The training itself is 2x per day, every day for many weeks. It takes a long time to regenerate nerves, so I tell people to continue the training for 6 months. For the session, you smell each jar for 15-20 seconds at a time. It’s important as you’re smelling to focus your memory on what that smell used to smell like. This is especially important for people who have parosmia, or distorted smell, because when they’re smelling something they may be getting a terrible smell, a chemical sense or a rotten smell. So for them it’s important to really focus on what the smell should be. That’s what can create the correct connections sent back to the brain.
It’s incredible that even 10 years ago we didn’t know that the adult mammalian brain had the ability to form new synaptic connections and remodel itself, but it does. We know that now and we can take advantage of that. We have functional MRI evidence showing what the brain looks like before someone with smell loss does olfactory training (it’s a disparate, chaotic array of things lighting up and none of it makes sense) and after olfactory training (just the olfactory cortex lights up). So with smell training you are functionally, organically changing the neural connections in the brain.
It’s important to remember to take small sniffs, not big inhales. Regular breathing through the nose is better. When you take big inhales you’re stimulating the trigeminal nerve receptors much more than the olfactory receptors in that case. And so you end up confusing the picture in the brain - you’re defocusing the input away from the olfactory input.
Note from Frauke, Certified Aromatherapist: it’s also important to recognize that when you inhale essential oil molecules there are actual, physical chemicals going up your nose and into your lungs. Inhaling too much essential oil can inadvertently irritate your lungs. That’s why I recommend little bunny sniffs which let the aroma molecules gently reach into the nose (not the lungs).
What should you think about when smelling each jar?
Frauke, FALK Aromatherapy: Because you’re doing the smell training twice a day, every day for at least 6 months, you can get bored thinking about the same thing day after day. So, besides thinking about the memory of the smell in that jar, think about the memory of an event from the past with that smell. Or think about the active use of that scent, the mechanical action (for example if you’re smelling lemon - think about peeling the lemon, squeezing the lemon, or zesting a lemon). I also encourage people to put a picture of the item they’re smelling in front of them to get the supportive visual recall.
Dr Patel: That’s a really important point because there’s actually scientific evidence that when people do olfactory training not just the olfactory cortex lights up, but also the visual cortex. That’s likely because when people are automatically focusing on what the scent used to smell like they’re also envisioning that smell. It’s a very natural thing for humans to do because we rely so highly on our sight. When we’re trying to remember the smell of something it’s almost an automatic thing that happens.
Who is smell training best suited for?
The great answer to that question is everyone. One of the wonderful things about olfactory training is that it's been studied in multiple etiologies (causes) of smell loss. It’s been studied in age-related loss, in trauma-related loss, in post-viral related loss (incl. COVID smell loss), and in neurodegenerative diseases such as Alzheimer’s and Parkinson’s. Smell training has proven itself to be beneficial, at varying levels, but to some amount, for each of these patient groups. So really anyone who has had any dysfunction in their ability to smell will most likely benefit from doing olfactory training.
What if you’ve had smell loss for a very long time? Can smell training still help?
That’s a tough one. Honestly it’s a tough conversation to have with patients because we never want someone to give up hope and to think that there’s nothing more that they can do. What I can say is that the two things that predict most if we can bring someone’s smell back is 1.) their age - the younger we are, the more likely we are to regenerate nerves in our body, including the olfactory nerves. And 2.) the duration of loss before a definitive intervention has taken place, like olfactory training.
It is tough when people have lost their sense of smell for 10 or 20 years. The shortest answer is probably not. It’s unlikely that after 10 years you’re going to be able to do something to get your sense of smell back. Now, there are a few caveats to that. For example, if someone’s loss is related to sinus or nasal inflammation, and they’ve had polyps in their nose for 10 years, those are people we can help to potentially get their smell back. It really depends on the cause of the loss. Something like post-traumatic smell loss 10 years out is much less likely to be able to be brought back. It doesn’t mean it’s impossible, but it is much less likely.
Generally speaking, from all of the scientific studies that have been done on smell loss, the longer you go without intervention (incl. smell training), even a year, there is a drop off to people responding to any intervention.
When should you start smell training?
I would say the sooner you can start, the better. I’m so grateful there are people like you out there who are there to support people with smell loss. Because it can be incredibly frustrating when you can’t smell anything, or it smells terrible, and you have to continue on for the length of time that’s required to regenerate those nerves and recreate the synaptic connections.
As motivation, I tell my patients to think about the fact that the longer they go without smell training, the less likely they’ll be able to do anything about it at a certain point. Really sticking with it, at the earliest possible moment, for 6 months gives them the best chance of bringing some smell back.
START EARLY AND BE CONSISTENT
What’s the goal of smell training?
There are three facets of smell health that we look for: odor identification, odor discrimination and odor threshold. One of the fastest ways we test for smell dysfunction in a clinical setting is through an odor identification test. I will say though that after patients come back 6 months later, after having done smell training, they tell me anecdotally that they can definitely pick up things more in their environment - different odors that they weren’t able to detect before. But when they do that identification test again, they don’t score that much differently than before. The reason for that is that threshold is actually one of the first things to come back. Which means that there’s still improvement taking place. We just haven’t tested for that particular facet. Being able to start picking up odors in your environment is the very first step of developing the entire olfactory ability again.
What happens biologically, and neurologically, when you do smell training?
Often when people have smell loss, or smell distortion, the problem is that the natural inherent regenerative process within the olfactory system has been damaged and stopped. Usually, if you haven’t had a large inflammatory or traumatic event to that system, about every 4-6 months you have turnover of all the olfactory neurons that are in your nose, and they’re replaced by new ones. This process takes place throughout our lifetime. The olfactory neurons are unique to all the other nerves in our body, and that’s what we’re trying to take advantage of.
The first key step in smell training is giving a continual structured input into the olfactory system, to try to wake back up that regenerative process. There are stem cells within the olfactory epithelium (that lining where the olfactory neurons are born and start growing) and they can send the signals to start that process of neuronal regeneration.
The second key step is for those neurons to make the right connections within the olfactory bulb, which sits right above the base of the skull at the base of the brain. The thin little neurons go through the thin plate of bones and the synapses connect to various glomeruli (bundles of nerves). You want them to connect in the right spot so you actually smell lemon when you hold lemon to your nose.
The third key step in the connective process is going from the bulb up to the olfactory cortex and synapse in the right connection.
Of course this is very simplified. There are millions of interneurons in that entire process: inhibitory neurons, modulating neurons, all kinds of neurons that are affecting the signal. That process is very complex. In order for that entire process to take place, that’s where the consistency and the duration become really important in smell training.
Does smell training even work?
I tell people in the clinic that it’s so simple that you think, how could this work? But yes, olfactory training has the highest level of evidence we use for any intervention in medicine - randomized, controlled trials. We’ve compared it to no intervention, just salt water rinsing, multiple placebos and we’ve found it to be effective.
The caveat to that is, unfortunately, it doesn’t help everyone. There are so many factors like age, duration of loss, other comorbidities (diabetes, high blood pressure, cardiovascular disease, etc.). There are other factors that are playing a role in whether or not those neurons in that system have the reserve to be able to bounce back after a large inflammatory insult. And so, unfortunately, it doesn’t help everybody. But I can say that in trials, where we’ve been able to enroll many patients, it has a significant benefit compared to placebo. So, yes, it is really doing something.
SMELL TRAINING IS NOT FOR EVERYONE, BUT IT HELPS MANY
When can people expect to start seeing results from smell training?
The sooner you get started after your initial loss, the sooner you will most likely find benefit. If it’s already been 6 months to a year since you lost your sense of smell, it will most likely take that same amount of time to see a major improvement. That’s why I usually don’t have people follow up until about 6 months after I see them because it can really take that long. I talk to my patients about not giving up, not getting discouraged, because they will likely go many months without seeing any significant improvement in their smell. But it doesn’t mean that it’s not coming. It just means that it takes a long time.
Does having parosmia mean that you’re on the way to recovery?
That is a common misconception. It is potentially a good sign because there are still olfactory neurons there to pick up some scent and send a signal back to the brain. So on that level it may be good.
However, I will say that parosmia can also be a negative sign. It’s showing that as the system is trying to recover, it’s not functioning properly. It can sometimes be a sign of worsening of the olfactory system.
The initial loss of smell isn’t going to give us a prognostication as to whether someone is going to get better, or worse, or stay the same. When people have parosmia it could go either way. It could show that they might be able to get through that and recreate the proper neural connections, or, unfortunately, it could show the opposite. Perhaps they’re scarred in the area where the nerve is supposed to go and they’re not able to go in that direction.
So, it’s not really a sign that it’s a good thing. It’s just another sign that there’s a dysfunction within the system.
Is smell training helpful for parosmia?
Yes, smell training is just as important for those with parosmia, as those with anosmia. Because that focusing of the memory of what the smell is supposed to smell like can really change this incorrect signaling pathway.
You see, the memory center is directly next to the olfactory center. That’s why when you walk down the street and you smell something, it can immediately take you back to a very vivid memory of the last time you smelled that smell. That’s because of that very immediate signaling that happens between the memory center and olfactory center in the brain. And you can utilize that proximity to try to change that aberrant signal, or pathway, and try to modulate that by trying to focus on the correct pathway.
I want to be clear, I don’t want people to think that just by thinking about normal smells they’ll be able to rewire the system. It’s a much more structured, organic change that you’re trying to make in your brain. It’s not that the bad smell is “all in your head.” It’s not that you can just wish it away. It’s not like that. It’s something where you have to practice to try to organically change the connections that are taking place. And that just takes time and a lot of attention and focus.
What are the biggest struggles you see patients having with smell loss?
The first thing is that it’s very impactful on you. It’s very difficult to explain to friends and family who don’t have that experience. And it’s made even more difficult by physicians who they go and see. They’re told that either “it’s not a big deal, just deal with it” or “there’s nothing we can do. You’re just going to have to live with it.” That’s very frustrating for patients and it makes them feel like they’re not being heard. They feel very alone. So, I would say that is the hardest thing that patients go through.
Just recognizing what a person with smell loss is going through can be a first step in helping to move to the next step.
JUST BELIEVE A PERSON WHEN THEY TELL YOU WHAT’S GOING ON
What if you don’t have an association with the 4 smells used in smell training?
It’s really important that you have a memory of the scents you’re training with. Don’t use scents you don’t have an association with. There are plenty to choose from within those categories. The most important thing is the memory. Really focusing on the memory of what that scent is supposed to smell like - that is the key.
Can intranasal vitamin A or intranasal steroids help along with smell training?
Intranasal steroids can be divided into a steroid spray (in the EU they’re drops) or an irrigation where you put steroids in a big volume of salt water and rinse the entire nose and sinuses.
The rinse we use here in the US, called Budesonide, has been shown to improve the efficacy of olfactory training. It’s a randomized trial I did. I also did a systemic review of all of the different ways we use steroids in the nose with patients who have smell loss, and steroid sprays like flonase, etc. don’t actually reach the olfactory cleft. They affect the front two-thirds of the nose and then just go down. So, those do not help people with smell loss. It’s really a waste of time.
Finally, there are oral steroids. If you get someone soon enough after a post traumatic or post viral event, it may be helpful. But it’s rare to see someone within the first week.
It’s a tough one and the jury is still out really. Because there are a whole host of side effects that come with oral or systemically absorbed steroids which you won’t get with the topical irrigation.
Finally, the intranasal vitamin A. At this point studies are not showing high efficacy. Perhaps with more data and more studies, maybe we will see some sort of benefit with that, but as of now there’s no clear benefit to using that.
Thank you very much for joining me, Dr. Patel.
LEARN TO MAKE SMELL TRAINING A HABIT
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