Smell Training to Help Restore Lost Sense of Smell

It was recently brought to my attention that olfactory training may help restore a lost sense of smell particularly after a viral upper respiratory infection or head trauma where no physical nasal obstruction is present. Olfactory training is analogous to physical therapy used to help restore limb movement after a stroke. Much of the basis found over the possible benefit of olfactory training stems from German research published in 2009 and later supported by a 2020 meta-analysis.

One group of patients (with lost sense of smell) performed the Training (n = 40), whereas another part did not (n = 16). Exclusion criteria for patients were sinunasal disease. Olfactory training was performed over a period of 12 weeks. Patients exposed themselves twice daily to four intense odors (phenyl ethyl alcohol: rose, eucalyptol: eucalyptus, citronellal: lemon, and eugenol: cloves). Olfactory testing was performed before and after training using the “Sniffin' Sticks” (thresholds for phenyl ethyl alcohol, tests for odor discrimination and odor identification) in addition to threshold tests for the odors used in the training process. [link]

What they 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.

The 2020 meta-analysis stated that:

Based on the available evidence, olfactory training is a recommendation for the treatment of post-viral olfactory dysfunction. The use of short‐term systemic and/or topical steroids is an option in select patients after careful consideration of potential risks of oral steroids. [link]

The nice thing with olfactory training is that you can easily do this at home.

You will need to purchase four different essential oils: lemon, rose, clove and eucalyptus. You can easily obtain them online or from aromatherapy stores. You will also need four small amber colored empty glass jars with lids to store and utilize during treatment sessions.

Pour some of the essential oil quarter-way up into the jar and/or saturate a disc of watercolor paper and place in the jar. Keep the lid screwed on tight in between treatment sessions. The reason you only partially fill the jar is to allow airspace over the liquid for volatile odor molecules to build up in order to improve availability for sniffing.

Step 1: Hold the first jar about an inch away. The order in which you smell the oils does not matter.

Step 2: Relax and try to perform tiny little "bunny sniffs" into the nose. Do not sniff too quickly or deeply otherwise the essential oil vapor will pass too quickly through the nose and down into the throat/lungs where it does no good. You want to allow adequate time for the smell to be contained within the nose.

Step 3: Try this a couple more times, but overall, there is no need to spend more than 10 seconds for each smell. Then rest for a minute to allow time for the smell to wash out of the nose.

Step 4: Move on to the next smell and repeat as above.

Step 5: Perform above steps 2 times per day for minimum 12 weeks.  You can do this for longer.

Some things to keep in mind...

Perform smell training during a quiet moment of the day without distractions while focusing on what smell you are trying to perceive. If the smell seems distorted, that is ok. Any type of smell perception is a good sign. Don’t smell train straight out of the original essential oil bottle as the small opening won’t give you a very powerful smell experience. That’s why jars are always recommended to use instead. Do keep your essential oil bottles in the fridge and away from sunlight to keep them fresh. Essential oils are expensive and have a limited shelf life. The jars used for treatment sessions should be kept at room temperature, but away from sunlight. Do change out the oils every 4-5 months. They should keep fresh during this time if you keep them tightly capped and out of the sun.

Why are these four particular fragrances used?

It's mainly based on data attempting to categorize smells the same way that tastes have been classified as being sweet, sour, salty and bitter. In 1916, a German psychologist Hans Henning developed a model for this which he called the ‘odour prism’, classifying smells as flowery (rose), fruity (lemon), spicy (cloves), resinous (eucalyptus), foul and burnt. In this way the olfactory system of the person undertaking the training is being stimulated by a wide range of different odor types. Foul and burnt are not typically used during olfactory training due to the unpleasant smell, though one can incorporate these odors as well.

Steroids, vitamin B, zinc, theophylline nasal spray, and α-lipoid acid have also been used to treat post-infectious olfactory loss, but thus far there is no definitive effective medical therapy available to date.

References:
Treatment of post‐viral olfactory dysfunction: an evidence‐based review with recommendations. IFAR. June 22, 2020.

Effects of olfactory training in patients with olfactory loss. Laryngoscope, 119:496–499, 2009

Modified olfactory training in patients with postinfectious olfactory loss. Laryngoscope , 125:1763–1766, 2015

Henning, H. (1916) Der Geruch. Barth, Leipzig.

A note on Henning’s smell series. Am. J. Psychol., 33, 423–25. 1922.

Further studies of Henning’s system of olfactory qualities. Am. J. Psychol., 35, 436–445. 1924