What Is Olfactory Training? A Complete Guide

What is olfactory training?

Olfactory training (also called smell training) is a structured practice of repeatedly exposing yourself to a specific set of odors over a sustained period of time. The goal of the practice is to engage the olfactory system through deliberate, focused sniffing sessions, typically performed twice a day.

The concept is rooted in a property of the olfactory system called neuroplasticity. The brain's ability to reorganize and form new neural connections. The olfactory nerve is one of the few cranial nerves with the capacity for regeneration, and researchers have studied whether structured odor exposure may support this process.

Olfactory training is not a medication, supplement, or medical device. It is a behavioral practice (similar in principle to physical therapy exercises) that individuals perform independently at home.

Where did olfactory training come from?

The modern concept of structured olfactory training was introduced in a 2009 study published in The Laryngoscope by Dr. Thomas Hummel and colleagues at the Smell & Taste Clinic, University of Dresden Medical School in Germany.

In this study, the researchers asked participants with olfactory loss to sniff four distinct odors (phenyl ethyl alcohol (rose), eucalyptol (eucalyptus), citronellal (lemon), and eugenol (clove)) twice daily for a period of 12 weeks. These four scents were selected because they each represent a different primary odor category, providing broad stimulation across the olfactory system. Olfactory function was assessed using the Sniffin' Sticks test, a standardized clinical tool that measures odor threshold, discrimination, and identification.

The study reported that participants who performed the training showed higher olfactory test scores compared to those who did not train. This research established the foundational protocol that has been used, adapted, and studied by other researchers in the years since.

Citation: Hummel T, Rissom K, Reden J, Hähner A, Weidenbecher M, Hüttenbrink KB. Effects of olfactory training in patients with olfactory loss. The Laryngoscope. 2009;119(3):496-499. doi:10.1002/lary.20101

What does the research say?

Following the 2009 study, multiple research groups have investigated olfactory training in different populations and with varying protocols. Below is a summary of key published studies. These summaries describe what the researchers reported in their papers; they are not claims made by The Olfactory Training Kit or Advanced Rx.

Konstantinidis et al. (2013). Post-Traumatic and Post-Infectious Olfactory Dysfunction

Researchers at the Smell and Taste Clinic at Aristotle University of Thessaloniki in Greece conducted a prospective study of 119 participants. Some with smell loss following upper respiratory infections and some with post-traumatic smell loss. Participants performed olfactory training with the same four-odor protocol (rose, eucalyptus, lemon, clove) over a period of 16 weeks, twice daily. Olfactory function was assessed using the Sniffin' Sticks test.

The researchers reported that participants in the training groups showed statistically significant improvements in their composite olfactory scores compared to the control groups. The study also examined whether the type of olfactory loss (post-infectious vs. post-traumatic) influenced outcomes.

Citation: Konstantinidis I, Tsakiropoulou E, Bekiaridou P, Kazantzidou C, Constantinidis J. Use of olfactory training in post-traumatic and postinfectious olfactory dysfunction. The Laryngoscope. 2013;123(12):E85-90. doi:10.1002/lary.24390

Damm et al. (2014). Randomized, Controlled, Multicenter Study

This was the largest controlled study of olfactory training at the time of its publication. Conducted across twelve university medical centers in Germany, the study enrolled 144 participants with post-infectious olfactory dysfunction (smell loss following an upper respiratory tract infection) lasting less than 24 months.

The study used a randomized, single-blind, controlled crossover design. Participants trained with either high-concentration or low-concentration odors, and olfactory function was assessed at baseline, 18 weeks, and 36 weeks using the Sniffin' Sticks test. The researchers reported that training with high-concentration odors was associated with greater improvement in olfactory scores than training with very low-concentration odors. This study was described in the literature as the first quasi placebo-controlled study examining the practice.

Citation: Damm M, Pikart LK, Reimann H, Burkert S, Göktas Ö, Haxel B, Frey S, Charalampakis I, Beule A, Renner B, Hummel T, Hüttenbrink KB. Olfactory training is helpful in postinfectious olfactory loss: a randomized, controlled, multicenter study. The Laryngoscope. 2014;124(4):826-831. doi:10.1002/lary.24340

Konstantinidis et al. (2016). Long-Term Effects

The same research group in Thessaloniki published a follow-up study examining whether longer durations of olfactory training were associated with different outcomes. This prospective study included 111 participants with post-infectious olfactory dysfunction. Two groups performed training for 16 weeks and 56 weeks respectively, and were compared with a control group. Training used the same four-odor protocol, twice daily.

The researchers reported that participants who trained for the longer duration showed greater improvements on olfactory testing. They also reported that participants who completed the shorter training protocol maintained their scores at the 56-week follow-up assessment.

Citation: Konstantinidis I, Tsakiropoulou E, Constantinidis J. Long term effects of olfactory training in patients with post-infectious olfactory loss. Rhinology. 2016;54(2):170-175. doi:10.4193/Rhino15.264

Meta-Analyses

Several systematic reviews and meta-analyses have aggregated data from multiple olfactory training studies. A 2016 meta-analysis published in the International Forum of Allergy & Rhinology by Pekala et al. pooled results from multiple controlled trials and concluded that the existing literature supported olfactory training as an option for individuals with olfactory loss. A more recent 2024 meta-analysis published in Rhinology by Liu et al. analyzed pooled data from eight previously published studies and reported that olfactory training was associated with improvements in olfactory function across multiple etiologies of olfactory dysfunction.

These meta-analyses reflect the state of the published literature; they do not constitute medical advice or a guarantee of individual outcomes.

How is olfactory training performed?

The standard olfactory training protocol, as described in the published studies referenced above, follows a consistent structure:

The odors. Four distinct scents are used, each representing a different primary odor category. The original protocol uses rose (floral), lemon (fruity), clove (spicy/aromatic), and eucalyptus (resinous). These categories were chosen to provide diverse stimulation across the olfactory receptor landscape. Some studies have explored using different or additional scents after an initial training period.

The routine. Participants in the clinical studies were asked to sniff each of the four odors for approximately 10 to 20 seconds per scent, twice per day, once in the morning and once in the evening. During each sniffing session, participants were encouraged to focus their attention on the odor and, if possible, attempt to recall memories or associations related to the scent.

The duration. The original Hummel (2009) protocol used a 12-week training period. Subsequent studies have explored both shorter and longer durations. The Konstantinidis (2016) long-term study used a 56-week protocol. Most published studies recommend a minimum of 12 weeks, and some researchers have suggested that longer training periods may be associated with further changes in olfactory test scores.

The environment. There are no special requirements for where training takes place. Published protocols suggest performing the practice in a comfortable, quiet setting where you can focus your attention on the scents.

What causes smell loss?

Olfactory dysfunction (a reduced or altered ability to perceive odors) is a common condition. Published estimates suggest that approximately 20% of the general population experiences some degree of olfactory impairment.

The medical literature describes several categories of olfactory dysfunction:

Anosmia refers to a complete loss of the ability to smell. Hyposmia refers to a partial reduction in smell ability. Parosmia refers to a distorted perception of odors, where familiar scents smell different than expected, often described as unpleasant. Phantosmia refers to perceiving odors that are not actually present.

Common causes of olfactory loss discussed in the medical literature include upper respiratory tract infections (such as the common cold, influenza, or COVID-19), head trauma, chronic sinusitis, nasal polyps, aging, exposure to certain chemicals, and neurodegenerative conditions. Post-infectious olfactory loss (smell loss that persists after recovery from an upper respiratory infection) is one of the most frequently studied categories in the olfactory training literature.

Why does oil quality matter for smell training?

The published research protocols consistently use high-quality, concentrated odorants. The Damm et al. (2014) multicenter study specifically compared training with high-concentration odors versus very low-concentration odors and reported different outcomes between the two groups, suggesting that the strength and purity of the scent stimulus is a relevant factor.

Essential oils vary widely in quality. The term "essential oil" is not regulated by any single governing body, and commercially available oils may be diluted with carrier oils, synthetic fragrances, or other additives that reduce scent concentration. Diluted or adulterated oils produce a weaker olfactory stimulus, which may not provide the same level of engagement with the olfactory system during training sessions.

Gas Chromatography/Mass Spectrometry (GC/MS) testing is the standard analytical method for verifying the chemical composition and purity of essential oils. GC/MS analysis identifies the individual chemical compounds present in an oil sample and their concentrations, confirming whether the oil matches the expected chemical profile for that species. Oils that have been verified through GC/MS testing provide a level of quality assurance that untested oils cannot offer.

Frequently asked questions

Is olfactory training a medical treatment? Olfactory training is a behavioral practice, not a medical treatment, drug, or medical device. It has been studied in clinical research settings, and the published studies are available in peer-reviewed medical journals. Individuals interested in olfactory training should consult with their healthcare provider, particularly if they are experiencing persistent smell loss.

How long before someone might notice changes? The published studies assessed participants at various time points, typically at 12-week, 16-week, and 56-week intervals. Individual timelines discussed in the literature vary. The researchers generally recommend sustained, consistent practice over a period of months.

Can anyone try olfactory training? The published studies have enrolled adults with various types of olfactory dysfunction. As with any health-related practice, individuals should discuss olfactory training with their physician or ENT specialist, especially those with underlying medical conditions, allergies to specific essential oils, or those who are pregnant or nursing.

What scents are used? The standard protocol uses four scents representing the primary odor categories: floral (rose or lavender), fruity (lemon), aromatic/spicy (clove), and resinous (eucalyptus). These specific scents were selected by the original researchers because they represent a broad spectrum of the olfactory landscape.

Does olfactory training work for everyone? The published research reports group-level statistical outcomes, not individual guarantees. Study results have varied across different populations and etiologies. Some participants in the published studies showed measurable changes on olfactory testing, while others did not. Factors discussed in the literature as potentially influencing outcomes include the cause of olfactory loss, its duration, and adherence to the training protocol.

References

1. Hummel T, Rissom K, Reden J, Hähner A, Weidenbecher M, Hüttenbrink KB. Effects of olfactory training in patients with olfactory loss. The Laryngoscope. 2009;119(3):496-499. doi:10.1002/lary.20101
2. Konstantinidis I, Tsakiropoulou E, Bekiaridou P, Kazantzidou C, Constantinidis J. Use of olfactory training in post-traumatic and postinfectious olfactory dysfunction. The Laryngoscope. 2013;123(12):E85-90. doi:10.1002/lary.24390
3. Damm M, Pikart LK, Reimann H, et al. Olfactory training is helpful in postinfectious olfactory loss: a randomized, controlled, multicenter study. The Laryngoscope. 2014;124(4):826-831. doi:10.1002/lary.24340
4. Konstantinidis I, Tsakiropoulou E, Constantinidis J. Long term effects of olfactory training in patients with post-infectious olfactory loss. Rhinology. 2016;54(2):170-175. doi:10.4193/Rhino15.264
5. Pekala K, Chandra RK, Turner JH. Efficacy of olfactory training in patients with olfactory loss: a systematic review and meta-analysis. International Forum of Allergy & Rhinology. 2016;6(3):299-307. doi:10.1002/alr.21669
6. Liu DT, Pellegrino R, Sabha M, et al. Olfactory training: a pooled analysis. Rhinology. 2024. doi:10.4193/Rhin24.131

This article is provided for informational and educational purposes only. It is not medical advice and is not intended to diagnose, treat, cure, or prevent any disease. The studies referenced above represent published scientific research; their inclusion does not constitute a claim that any product will produce the same results. Please consult a qualified healthcare provider for advice about your individual health situation.

The Olfactory Training Kit is assembled at Advanced Rx, a licensed pharmacy in Fort Washington, Pennsylvania.