How Long Does Olfactory Training Take to Work?

Why people ask this question

For someone experiencing smell loss, one of the first things they want to know about any potential approach is how long it takes. This is an understandable question, but it does not have a single, simple answer. The published research on olfactory training provides data on group-level outcomes measured at specific time points. It does not provide individualized timelines.

What the studies do offer is a general framework: the minimum training periods used in clinical research, the time points at which researchers have measured changes, and the factors that the literature suggests may influence outcomes.

What the original study used: 12 weeks

The foundational olfactory training study by Hummel et al. (2009) at the University of Dresden Medical School in Germany used a 12-week training protocol. Participants with olfactory loss sniffed four odors (rose, eucalyptus, lemon, and clove) twice daily for the full 12-week period. Olfactory function was assessed before and after the training period using the Sniffin' Sticks test, a standardized clinical tool that measures odor threshold, discrimination, and identification.

The researchers reported that participants who completed the 12-week training protocol showed higher olfactory test scores compared to a control group that did not train. This study established 12 weeks as the baseline duration referenced by most subsequent research.

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

Subsequent studies and their timelines

Following the original protocol, other research groups have studied olfactory training using both similar and extended durations. Below is a summary of the timelines used in key published studies.

Konstantinidis et al. (2013), 16 weeks

Researchers at Aristotle University of Thessaloniki in Greece conducted a prospective study of 119 participants with post-infectious and post-traumatic olfactory loss. The training protocol followed the same four-odor, twice-daily approach over a period of 16 weeks. Olfactory function was assessed at baseline and at 16 weeks using the Sniffin' Sticks test.

The researchers reported statistically significant improvements in composite olfactory scores among trained participants compared to control groups at the 16-week assessment.

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), 18 and 36 weeks

The largest controlled study at the time of its publication was conducted across twelve university medical centers in Germany and enrolled 144 participants with post-infectious olfactory dysfunction. This randomized, single-blind, controlled crossover study assessed participants at baseline, 18 weeks, and 36 weeks.

The researchers reported that training with high-concentration odors was associated with greater improvement in olfactory scores than training with very low-concentration odors. Notably, this study included a 36-week assessment point, providing data on outcomes at a longer time horizon than most earlier studies.

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), 16 weeks vs. 56 weeks

This follow-up study specifically examined whether training duration influenced outcomes. The researchers enrolled 111 participants with post-infectious olfactory dysfunction and compared groups who trained for 16 weeks and 56 weeks against a control group.

The researchers reported that participants who trained for 56 weeks showed greater improvements on olfactory testing than those who trained for 16 weeks. They also reported that participants who completed the shorter 16-week protocol maintained their scores when assessed again at 56 weeks, suggesting that improvements observed during training were sustained even after the formal training period ended.

This study is frequently referenced in the literature as evidence that longer training durations may be associated with further changes in olfactory function.

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

What the meta-analyses say about duration

Systematic reviews and meta-analyses have attempted to aggregate data across multiple olfactory training studies to draw broader conclusions.

A 2016 meta-analysis by Pekala et al. published in the International Forum of Allergy & Rhinology pooled data from multiple controlled trials. The analysis concluded that the existing literature supported olfactory training as an option for individuals with olfactory loss, though the authors noted variability in study designs and training durations.

A 2024 meta-analysis by Liu et al. published in Rhinology analyzed pooled data from eight previously published studies. The authors reported that olfactory training was associated with improvements in olfactory function across multiple etiologies. This more recent analysis included studies with a range of training durations, reflecting the broader body of evidence that has accumulated since 2009.

Neither meta-analysis identified a single optimal training duration. The data across studies suggests that 12 weeks is the minimum period that has been studied, with some evidence pointing toward continued changes with longer practice.

Why 12 weeks is considered the minimum

The 12-week duration is not an arbitrary number. It reflects the timeline used in the original Hummel (2009) study and has been adopted as the standard minimum in subsequent research protocols. Several factors likely contribute to why this timeframe was chosen and has persisted in the literature:

Olfactory neuron turnover. The olfactory epithelium (the tissue in the nasal cavity that contains olfactory sensory neurons) undergoes a natural cycle of cell turnover. Published research indicates that olfactory sensory neurons are replaced on a cycle of approximately 30 to 60 days. A 12-week training period encompasses at least one full cycle of this turnover, providing a biologically plausible timeframe for structured odor exposure to interact with newly generated neurons.

Neuroplasticity timelines. Research on neuroplasticity in other sensory and motor systems suggests that measurable structural and functional changes in the brain typically require weeks to months of sustained practice. The 12-week minimum for olfactory training is consistent with timelines observed in rehabilitation research more broadly.

Study design considerations. From a research methodology standpoint, 12 weeks provides a sufficient window to observe group-level changes while maintaining reasonable participant adherence. Shorter studies would risk missing changes that develop gradually; excessively long studies increase dropout and confounding variables.

Factors the literature discusses as potentially influencing timelines

The published research identifies several variables that may affect how olfactory training outcomes vary across individuals and study populations. These are factors discussed by the researchers in their papers. They are not claims about any specific product.

Cause of smell loss. Studies have enrolled participants with different etiologies, including post-infectious olfactory loss (following colds, flu, or COVID-19), post-traumatic loss (following head injury), and idiopathic loss (no identified cause). Some studies have reported different response patterns across these groups. Post-infectious olfactory loss is the most commonly studied category and has the largest body of published data.

Duration of smell loss before beginning training. Several studies have noted that participants with a shorter duration of olfactory loss prior to beginning training showed different patterns on olfactory testing compared to those who had experienced smell loss for longer periods. This factor is frequently mentioned in the literature as potentially relevant.

Adherence to the protocol. The published studies ask participants to train twice daily, every day, for the full study duration. Researchers have noted that adherence (consistently performing the training as prescribed) is an important variable. Studies that measured adherence reported that more consistent practice was associated with better outcomes on olfactory testing.

Age. Some studies have reported that participant age may be associated with different outcomes. The olfactory system undergoes natural changes with aging, and the regenerative capacity of olfactory neurons may differ across age groups.

Odor concentration. The Damm et al. (2014) multicenter study specifically tested whether the concentration of training odors influenced outcomes and reported that higher-concentration odors were associated with greater improvements in olfactory scores compared to very low-concentration odors.

What "working" means in the research context

It is worth clarifying what published studies measure when they report that olfactory training "works." The studies do not typically measure whether a participant's subjective experience of smell returned to normal. Instead, they measure changes in standardized olfactory test scores, primarily using the Sniffin' Sticks test, which generates a composite score (called the TDI score) based on three components: odor threshold (the faintest concentration detectable), odor discrimination (the ability to distinguish between different odors), and odor identification (the ability to name or recognize odors).

A statistically significant improvement in TDI scores at the group level does not necessarily mean that every individual in the study noticed a subjective improvement in their daily life. Conversely, some individuals may notice subjective changes that are not fully captured by standardized testing. The studies report what was measured using their chosen instruments.

This distinction is important for setting expectations. Olfactory training is studied as a practice that may produce measurable changes on clinical testing over time, not as a guaranteed restoration of normal smell function.

A realistic framework for expectations

Based on the published literature, here is what the research collectively suggests about timelines, framed as what the studies have reported, not as predictions for any individual:

Weeks 1–4: The published studies do not typically report assessment data for this early period. This is the phase where the practice is being established as a daily habit. Researchers do not generally describe measurable changes at this stage.

Weeks 4–12: Some studies have included interim assessments during this window. The data at these time points varies across studies. The 12-week mark is the earliest point at which the original protocol was designed to assess outcomes.

Weeks 12–16: This is the primary assessment window for most published studies. The majority of reported data on training outcomes comes from evaluations conducted at 12 to 16 weeks.

Beyond 16 weeks: The Konstantinidis (2016) long-term study provides the strongest data for extended training periods, with assessments at 56 weeks. The researchers reported that continued training beyond 16 weeks was associated with further improvements on olfactory testing.

Frequently asked questions about timeline

Can olfactory training produce results faster than 12 weeks? The published studies were not designed to measure outcomes before 12 weeks in most cases. There is limited published data on whether measurable changes occur earlier. Some researchers have noted that individual participants reported subjective changes before formal assessment points, but these anecdotal observations are not the same as controlled study data.

Is there a point where continuing training no longer helps? The longest controlled study duration in the published literature is 56 weeks (Konstantinidis 2016). There is no published data establishing an upper limit beyond which continued training has no further association with olfactory test score changes. Some researchers have suggested that training may be beneficial as an ongoing practice, but long-term data beyond one year is limited.

What if I don't notice any changes after 12 weeks? The published studies report group averages, and not all participants in the studies showed measurable improvement. Researchers have suggested that individuals who do not observe changes after an initial training period may consider continuing for a longer duration, switching to different scents to provide novel stimulation, or consulting with an ENT specialist or otolaryngologist for further evaluation. These are suggestions discussed in the literature, not prescriptive medical advice.

Should I track my progress? While not a formal component of the published research protocols, some clinicians and researchers have suggested that keeping a simple log (noting any changes in odor perception, even subtle ones) can be useful for individuals undertaking olfactory training. This is a practical suggestion discussed in clinical guidance, not a studied intervention.

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, 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
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.