Research Studies and Articles

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Professor Thomas Hummel's 2009 Study

In 2009, Professor Thomas Hummel at the University of Dresden in Germany, conducted a study to see if repeated exposure to certain scents over a three month period would have any effect on the olfactory ability of anosmia (complete loss of smell) patients. The study can be viewed here

The research study conducted involved two groups of people suffering from anosmia due to head injuries, upper respiratory infections, or idiopathic smell loss. One of the groups were given four essential oils and were told to sniff them every morning and night, for ten seconds each, for twelve weeks. The other group acted as the control group and were not given any essential oils. At the end of the twelve weeks, Professor Hummel found that 30% of the test group reported improvement in their smell, while none of the control group saw improvement. Olfactory function increased in patients effected by smell loss from head injuries, respiratory infections, and idiopathic olfactory loss.

The four fragrances that Professor Hummel used in his study were Rose, Lemon, Clove, and Eucalyptus. These have been used in various other studies. The "Odor Prism", coined by German psychologist Hans Henning, is a model to classify smells into flowery, foul, fruity, spicy, burnt, and resinous. Professor Hummel picked his scents to correspond with four of these categories: Flowery- Rose, Spicy- Clove, Fruity- Lemon, Resinous- Eucalyptus

Smell Training Improves Olfactory Function and Alters Brain Structure

Al Aïn S, Poupon D, Hétu S, Mercier N, Steffener J, Frasnelli JSmell training improves olfactory function and alters brain structure. Neuroimage. April 2019 ;189:45-54doi: 10.1016

This study investigated the effects of smell training on olfactory function and brain neuroplasticity over a six week time period. Thirty-six people were randomly placed into three groups. One group underwent intense smell training of at least 20 minutes and included an odor classification task, odor quality task, and a target odor detection task. The second group went through the same training except only visually, and the third group did not participate in any of the smell training. Before and after the study, all patients went through an olfactory test. The conclusion of the study found that the group that underwent smell training improved in olfactory function especially in smell recognition. Intensive olfactory training generally can improve olfactory function and help restore smell, as well as improve associated areas of the brain.

More Studies & Articles about Smell Training

Exposure to Odors Improves Olfactory Function in Healthy Children (here)

Mori E, Petters W, Schriever VA, Valder C, Hummel T. Exposure to odours improves olfactory function in healthy children Rhinology. 2015 Sep;53(3):221-6. doi: 10.4193/Rhin14.192.


Effectiveness of Olfactory Training on Different Severities of Posttraumatic Loss of Smell (here)

Pellegrino R, Han P, Reither N, Hummel T Effectiveness of olfactory training on different severities of posttraumatic loss of smell. Laryngoscope. 2019 Mar 8. Aug;129(8):1737-1743. doi: 10.1002/lary.27832. Epub 2019 Mar 8.


Efficacy of Olfactory Training in Patients with Olfactory Loss (here)

Pekala K, Chandra RK, Turner JH. Efficacy of olfactory training in patients with olfactory loss: a systematic review and meta-analysis. Int Forum Allergy Rhinol. 2015; 00:1–7


Long Term effects of Olfactory Training in Patients with Post-Infectious Olfactory Loss (here)

Konstantinidis I, Tsakiropoulou E, Constantinidis J Long term effects of olfactory training in patients with post-infectious olfactory loss; Rhinology 54 - 2 2016; Article 4412.


Modified Olfactory Training in Patients with Post-Infectious Olfactory loss (here)

Altundag A, Cayonu M, Kayabasoglu G, Salihoglu M, Tekeli H, Saglam O, Hummel T. Modified olfactory training in patients with post-infectious olfactory loss Laryngoscope. 2015 Aug;125(8):1763-6. doi: 10.1002/lary.25245. Epub 2015 Jun 2.