COVID-19: loss of smell and taste

Carl Philpott is professor of rhinology and olfactory at University of East Anglia, he even established the first UK smell and taste clinic. Throughout the pandemic he has seen a dramatic increase in patients, some of which are surprising. He tells Harry Lewis and Julia Ravey what he has witnessed over the past two years and what new research is on the horizon... 

Harry - Carl, can we start off by trying to distinguish between taste and flavor?

Carl - Yes. So flavour is really the combination of smell and taste together. Whereas taste, from a medical perspective, is simply what we experience from the tongue and the other locations of taste buds in the mouth and throat.

Harry - And is there a way for us to do this in the studio for us to distinguish between these two?

Carl - Absolutely, yes. So we can do something called the Skittle test.

Harry - I have a big pack of Skittles here with me. Let me quickly hand one over to Julia as well, whilst we're here: it’d be rude to leave her out. What do we do next, Carl?

Carl - Okay. So the first thing is to pinch your nose so that there's no air flowing through your nose. And then when you've done that you can place the Skittle inside your mouth. Let it sit there for five to 10 seconds just to sort of start dissolving and get an idea of what it is you're tasting.

Julia - Sugar?

Carl - Sugar. Yeah. It's very sweet. Isn't it?

Harry - Very specific to one part of my tongue as well.

Carl - If you release your hand from your nose to let the air flow through your nose, you should now experience what the flavor of the sweet is.

Harry - Oh yeah. It's fantastic. I've been waiting to eat these all show as well, Carl. So suddenly I'm getting that blueberry-ness come through and it's fantastic. What about you, Julia?

Julia - Yeah. Yeah, the orange is there.

Harry - It's around the whole mouth as well. That's what I'm experiencing: it's not just on the tongue, but it's actually kind of coating the inside of my mouth.

Carl - What's happening now is you've got a process that we call retronasal olfaction taking place. That's basically the smell of the food inside your mouth, and you're breathing it back out through your nose from the back of your mouth. So it's the reverse of when you sniff things from the outside.

Harry - And for people with parosmia what's happening?

Carl - For parosmia obviously they're getting the same signal that you and I would get in normality, but the information as it's picked up in the smell receptors is then being interpreted incorrectly. We think that's largely because some of the smell receptors aren't working properly, so you're only getting part of the jigsaw. It's always unpleasant generally, unfortunately. I don't know why it's unpleasant. A few people get pleasant parosmia, but most people get unpleasant parosmia.

Harry - Now that you're saying a few people are getting it. How many people are we seeing, since COVID began, develop these symptoms? Is it a lot?

Carl - It is. Of the people who get infection with COVID-19 about 60% get smell and taste loss as a symptom. Of those about 10 to 15% go on to have persistent symptoms that last more than four weeks. So if you multiply that by the number of infections we've had in the UK so far, we're talking somewhere close to a million people. Of those million people, we think about 50% of those, based on the work of our global studies, are getting parosmia: this smell distortion. If you look at them six months on from the time of their original infection, increasingly we see more and more younger people and now children being affected by these smell disorders. And for the first time I've been seeing teenagers in my clinic, which I've never seen teenagers with viral smell loss in the last two decades. So that's already a new phenomenon that COVID has produced.

Harry - How many are we talking about?

Carl - Well, I could only say one or two a month at the moment, but given that I'd never seen them before that's quite significant. And also through our charity, Fifth Sense, we get a lot of people getting in touch with the charity, looking for support, and again, the parents of children and some are even under the age of 10. So it's surprising how young some of these people are being affected, which is incredible.

Harry - I wonder what people that are suffering can do. I know there's been a lot of talk about smelling oils and I have a short clip of Claire again, giving it a go at home.

Claire - One thing I've been doing since I lost my smell and taste, probably about six weeks in, is smell training. So I basically just purchased a set of 20 oils, essential oils from Amazon and effectively what I do a couple of times a day, morning and evening just take short sniffs off each of the oils. I guess when I have bad weeks, I tend to not do it so often. And when I feel a bit more focused then I do sort of try it. The one thing I find discouraging is that I rank the smells, the bottles in the box, based on how well I can smell them. And it's interesting that over time, very few have moved up the scale and most of them have largely stayed in the same ranking. For example, smells like bergamot, rosemary and ginger I can't really smell in the essential oils. Then cinnamon, clove, eucalyptus, and lemon grass are probably the strongest sense. I also wander around the house, smelling things from the herb shelf; I'll smell toiletries, and there are certain things I'll sort of keep smelling just to sort of check back in. I must admit, I do get quite excited when I get a bit of a stronger smell because the one thing I have noticed is there's not much depth in a lot of the smells. So when I do find something that there's some depth in the joy, it's just unbelievable. I just try and continue to do this as regularly as I possibly can.

Harry - That was Claire there talking about the different essential oils that she's been smelling. Carl, for those people that are suffering, is this something they should be doing or is there certain treatments they can be doing at home?

Carl - So, yes. Smell training is an established rehabilitation technique that's had good evidence over the last 10 years. It doesn't work for everybody, but it's worth a try because it's simple to do. And the key message is you don't need to go out and buy anything expensive to do it. The things in your cupboard can be used to help you do it. The central message is four things, twice a day for one or two minutes. They should be things that you were familiar with before you had your problem. If you go to the Fifth Sense website, our charity's website, there's lots of information there about how you can go and do this on a simple and easy basis every day. But it's sticking with it. You've really got to stick with it for up to a year. In reality, the real studies show that the benefits come from longer-term determination with the technique and changing the smells every three months.

Harry - Carl, Claire wants to know she's been now with an altered sense of smell for a year. Is phantosmia something she's likely to have to live with the rest of our life?

Carl - These smell distortions like parosmia, and phantosmia tend to be self limiting. There is a range, but they do tend to get better with time. So they tend to sort of fade out. I'm always talking to people about, once the problem's gone beyond three months and it looks like it's a fairly established problem, then it's worse engaging with treatment, whatever that treatment may be. The biggest problem we have in this field is that there's a real paucity of good quality clinical trials to underpin any treatments. So most of the things that have been tried have been done so in studies that don't really have the sufficient scientific rigor, and that's one of the things I'm trying to correct. So it does tend to get better, but it is pretty miserable while people are experiencing it.

Harry - And Carl, is there any other research on the horizon that people might be using for treatment in the future?

Carl - Yes. So we are just about to start a trial using Vitamin A drops and that's a three month course of treatment. We're looking, compared to a placebo, to see if there are changes in the brain in the areas where smell signals are received as a consequence of doing so. Hopefully we'll take that into a further trial if that's successful.

Harry - Why Vitamin A?

Carl - The retinoic acid component of Vitamin A is potentially involved in the DNA repair process, allowing the receptor cells to potentially regenerate.