Is smell training a cure for post-viral smell loss? No, but...

Is smell training a “cure” for anosmia?

Smell training is a relatively new therapy for post-viral anosmia, first described in 2009 by Professor Thomas Hummel of the University of Dresden in 2009. While it has been extensively tested on subjects who lost their sense of smell after a virus (called post-viral anosmics), there is also some evidence to suggest that smell training can be of use to those anosmics who lost their sense of smell after a head injury. In both cases, smell training is only of use to patients who have begun to experience some recovery to the damaged nerves. This might mean distorted smells, or faint whiffs of smells.

The treatment options for anosmics have always been limited. Ear nose and throat surgeons (ENTs) have a small number of options with which to help patients, each geared to the individual’s case. Patients will be different, because there are a number of ways to lose your sense of smell. It is important therefore to seek a doctor’s advice when considering a new therapy.

Does smell training offer a “cure” for anosmia? In a word, no. It is no more a cure than physiotherapy is a cure for someone recovering from a stroke.  But like physio, smell training can build on your sense of smell if some level of natural recovery has occurred. Let’s look at this a bit more closely.

The little patch of cells at the top of your upper airway (the olfactory cleft) that relay the smell messages to your brain is called the olfactory epithelium.  When a bad virus damages these cells, the olfactory nerve is damaged and can’t do its job. It is no longer relaying information to the brain.  Imagine the telephone exchange, where all the wires that link your street to the outside world, get unplugged and are now lying in a heap on the floor. People are trying to ring in, and no one is answering. 

With the passage of time, many patients find that the wires slowly reconnect themselves. Sometimes the reconnection is complete, which would signal a recovery for the patient. If the reconnection is incomplete, or still going on, smells might be distorted, or only faint. Sometimes they are very unpleasant as regeneration begins– this can be extremely distressing for the people experiencing it, and may affect the patient’s ability to eat. 

While there are a number of studies that have looked at how patients fare over time using smell training, it is still not well understood just how smell training works. I believe that patients are in fact responding to the stimulus of smell training in the same way that perfumers respond to the kind of smell training required of them to become perfumery “noses”: repeated exposure to the stimulus of different smells; smelling in a way that is attentive, not passive; challenging the sense of smell to differentiate, seek resolution, and explore. These kinds of challenges are actually brain training. We smell, after all, with our brains, not just our noses. 

So what does this mean for a person struggling to cope with the devastating loss of smell after a virus? I would ask you, in the first instance, to take a simple test. You will need a friend to help you, a blindfold, and three different kinds of juice. Have your helper blindfold you, and offer you the three juices. Smell first, then taste. Can you say anything about the difference between the three?  Shuffle them and try again. Many people report that they can “smell nothing” or “taste nothing” but in fact they do have some limited ability to discern one from the other.

If the nerves in your nose have recovered even a bit, and you can differentiate these things, I suggest you try smell training. 

So let me give you another analogy to help you understand what I think happens when you start to smell train. Imagine your sense of smell is a garden full of beautiful multicoloured flowers. One day a virus comes, which acts like weed-killer, and kills everything, leaving scorched earth behind. Then, in time, a few things that look like weeds start to grow. They are not attractive and they make your garden ugly. But if you nurture these small plants, water them and feed them, and help them to be the strongest best plants that they can be, and then you divide them and replant them around your garden, you can do your best to help your garden regrow. Not only that, but the fertiliser on the ground may be helping other little seeds that were lying fallow. The more you water, feed and attend, the better your garden will grow. Crucially: your experience of your garden will be greater than that of the patient who has ignored their scorched garden, and never visited it again after smell loss.

This brings me to a final point about smell loss. It has been my own experience that smell loss got me out of the habit of seeking to smell things. I stopped asking myself, “can I smell this spring morning?”, “what, if anything, does this apple taste like?”, “can I smell this newspaper?”. Our brains seem to quickly lose the habit – and the talent – for this impulse. I am not talking about the functionality of the nose here, but the part of the brain that asks us to think about smell. To go back to the analogy of the telephone exchange, yes, the cables are in a mess on the floor, but what if you forget how to dial the phone? This is another reason why I think that smell training is so important. It keeps us focussed on seeking smell.  

You will find other posts on this website here to help you understand the actual method of smell training.

There is a list of peer-reviewed scientific articles here so that you can read for yourself what researchers have to say about smell training and other aspects of anosmia.