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The idea that our sense of smell can be improved via training might at first seem strange, but the more you think about it the more it makes sense.  Going to the gym and lifting weights can improve muscle mass and tone, and practising the guitar regularly will (hopefully!) improve proficiency.  So will spending time sniffing odours therefore improve one’s ability to detect them?

In recent years there have been a number of studies that have shown this to be the case.  For example, in 2011 researchers Jane Plailly and Jean-Pierre Royet demonstrated that similar areas of the brain are stimulated when both detecting and imagining particular scents.  Their subjects were both professional perfumers and students from ISIPCA, a college in France that trains perfumers.  Individuals were placed in an MRI scanner and asked to imagine the smell of a particular substance, the name of which appeared on a screen in front of them.  Plailly and Royet found that the level of activity in the brain actually decreases with the experience of the person being tested – essentially, the brains of more experienced, expert perfumers have to work less hard to imagine particular odours due to the training that they have undertaken.

The fragrance industry is, of course, dependent on the sense of smell and fragrances are developed by ‘trained smellers’, aka perfumers,  who spend years smelling and learning the scents of a huge variety of fragrance ingredients.

Can smell training benefit people who have suffered olfactory loss?

A number of studies have been done in recent years (see ‘Research Studies’ below for a list) which suggest that ‘smell training’ – repeated short-term exposure to odours – can potentially be of benefit to people who have been affected by olfactory loss, particularly those who have lost their sense of smell as the result of a virus such as the common cold.

Prof Hummel’s 2009 study

In 2009 Professor Thomas Hummel, who runs the Smell and Taste Clinic at the University of Dresden in Germany, ran a study to investigate whether repeated short-term exposure to odours over a twelve week period would have any effect on the olfactory ability of a group of anosmia sufferers.  An abstract of Prof. Hummel’s paper can be viewed here.

The study involved two groups of people with anosmia, all of whom had lost their sense of smell through either head trauma, severe infection of the upper respiratory tract, or for reasons unknown (idiopathic). One group was given four essential oils – rose, eucalyptus, clove, lemon – and told to sniff each one every day, morning and evening, for ten seconds at a time over a period of twelve weeks. The other group did not participate in the olfactory training. Both groups were tested at the beginning and then at the end of the twelve week period using sniffin’ sticks. What Prof. Hummel found was that a number of patients who had undergone the training (30% of the test group) experienced some improvement in olfactory function, compared to the group who had not participated.  Improvement occurred in patients who had suffered smell loss due to upper respiratory tract infection, head trauma and idiopathic olfactory loss.

2015 study: ‘Modified Olfactory Training’

In 2015 a further study was published which showed that smell training is potentially beneficial for people with impaired sense of smell due to a previous upper respiratory tract infection, and that some additional benefit can be gained from using a wider range of odours over a longer period than the 12 weeks used in earlier studies. The work was done at the Istanbul Surgery Hospital by a team including Professor Thomas Hummel and was reported in the Laryngoscope journal.

You can read a summary of the paper published in the Laryngoscope journal here.

What does this mean for someone affected by anosmia or hyposmia?

The results of the various research studies does give some hope for people affected by olfactory loss.  We’ve been in touch with Fifth Sense members who have had success with smell training, sometimes alongside a clinical intervention.  In many cases the training has, potentially, helped people to detect other scents in their environment, rather than just the scented oils used in the training.

There are lots of unknowns, however.  There is no evidence to show that smell training alone can bring about recovery of the sense of smell.  Perhaps the best way to think of it is as an aid to olfactory ability.  It is thought that smell training may help the regeneration of the olfactory receptor neutrons, but this  has yet to be proven.  Further research needs to be done in this area, but these studies do help demonstrate that the sense of smell in animals and humans has the ability to change and recover.  The chance of any recovery is likely to depend on the degree of damage caused, whether by a virus, head injury, or other factor.

We would recommend that smell training should not be viewed as a substitute for medical examination and treatment, where such is available, (click here for details of clinics we have links with), but rather as an accompaniment to any prescribed treatment.

I suffer from anosmia or hyposmia – how do I try smell training?

What you need:

  • Four different essential oils.  Lemon, rose, clove and eucalyptus are the four smells used in many of the published research studies.  You can obtain them online or from aromatherapy stores
  • Four empty glass jars with lids, or cotton pads, or fragrance strips

If using jars, pour some of the essential oil into the jar.  Keep the lid screwed on in between training sessions. The jar method is the one used in existing studies, the physics behind it is to allow an airspace over the liquid for odour vapour to build up and improve availability of volatile odour molecules.  Using cotton pads or fragrance strips is fine too.  If you are using jars then you can ignore the first two steps below.

1 – Pour a few droplets of one of the oils on to a testing stick or pad

2 – Do not try to sniff the stick/pad immediately; leave it for a few minutes for the fragrance to develop

3 – Hold the first jar, pad or fragrance strip up to your nose, about an inch away.  The order in which you smell the oils does not matter

4 – Relax and try to inhale naturally through the nose – sniffing too quickly and deeply is likely to result in you not being able to detect anything

5 – Try this a couple more times, then rest for five minutes

6 – Move on to the next smell and repeat as above.

Tips

  • Smell train at least twice every day, ideally morning and evening
  • Relax and inhale naturally
  • Don’t sniff too hard or for too long…10 seconds for each smell is enough
  • Try smelling other things too…spices in the cupboard, flowers in the garden, fragrances…anything that is safe to smell!
  • …And try to stick with it.  If you cannot smell anything at first then do not be disheartened.  Everyone is different, and we’ve heard from people who have tried this process themselves and have experienced varying degrees of success.  For some people it can take weeks or even longer before they detect anything, and some people may not get any benefit from it at all, but it is worth trying.

Just remember that the studies we have talked about here have shown that the sense of smell can change and recover, and that it can be trained and developed with exposure to odours, as expert perfumers will testify.  Good luck!

The Smells

It is worth briefly mentioning why Prof. Hummel chose the four particular fragrances used in his 2009 study (which have been used in many subsequent studies).

Attempts have been made to categorise smells, in the same way that tastes have been classified as being sweet, sour, salty and bitter.  In 1916 German psychologist Hans Henning developed a model for this which he called the ‘odour prism’, classifying smells as flowery, foul, fruity, spicy, burnt and resinous.  Prof. Hummel chose scents to represent four of these categories (or if you like the range of smell) for his study, as shown below.  In this way the olfactory system of the person undertaking the training is being stimulated by a range of different types of odours.

Flowery – Rose

Fruity – Lemon

Spicy – Cloves

Resinous – Eucalyptus

 

If you do decide to undertake this yourself then we would like to hear from you; please emailinfo@fifthsense.org.uk and tell us about your experience as it may be beneficial to others

Smell Training Q&A

Where can I buy the smells used in smell training?

The easiest smells to use are essential oils, which come in a wide variety of aromas.  They can be purchased online and from aromatherapy shops.  A quick online search will bring up places you can buy them from.

Does it matter which smells I use?

Many of the smell training research studies have used the same four smells – lemon, rose, clove and eucalyptus.  However there’s no evidence to say these are the ‘right’ smells to use.  Choosing smells that you are familiar with and have memories of is a good idea.  You could certainly start with these, and change them regularly – see the next question.

Why change the smells?  

One group of participants in the 2015 ‘Modified Olfactory Training’ study (see main page text) changed to a different set of four smells every twelve weeks.   The study suggests that this can potentially enhance success rates (note that the study was focused on people with post-viral olfactory loss).

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