Effects of olfactory training: a meta-analysis.

The neural plasticity of the olfactory system offers possibilities of treatment in terms of stimulation of the sense of smell, and different studies have suggested effectiveness of smell training, i.e., daily exposition to certain odors. To obtain reliable and precise estimates of overall treatment benefit on the olfactory function, we meta-analyzed the effects of smell training reported in 13 previous studies. We analyzed the smell training effectiveness across three different olfactory abilities, smell identification, discrimination and threshold for odor detection. We found a significant, positive effect of olfactory training for all olfactory abilities, with large effects of training on identification, discrimination and TDI-score and small-to-moderate effect in the case of threshold for odor detection. Interestingly, the pattern of results differed across Sniffin Sticks subtests depending on the origin of participants smell disorder, and the smell training duration influenced its effectiveness in the case of identification and the TDI score. Although the exact mechanism of olfactory recovery following the smell training still requires further investigation, our meta-analysis showed that such training should be considered an addition or alternative to existing smell treatment methods.