Essential Oils, Henning's Odor Prism, and Vagal Tone (Heart Rate Variability)
- Paul Rooney
- Jul 31
- 2 min read
Humans have long used aromatic oils for healing and mood, but a systematic framework for scents was first proposed by German psychologist Hans Henning in 1916. Henning’s “Odor Prism” identified six primary odor categories – Flowery, Fruity (Ethereal), Spicy, Resinous, Burnt, and Putrid. Modern olfactory training and therapy often focus on four pleasant categories (floral, fruity, spicy, resinous), deliberately omitting the unpleasant “putrid” and “burnt” odors line with this, my approach uses a set of essential oils spanning floral (e.g. geranium, jasmine), fruity (bergamot), spicy/herbaceous (rosemary), and resinous (cedarwood, frankincense) scents. This covers the breadth of the odor spectrum based on Henning’s theory, excluding only the noxious putrid/burnt notes.
Essential Oils and Vagus Nerve (HRV) – Evidence-Based Insights
Inhaled essential oils can influence the autonomic nervous system through olfactory–limbic pathways, which is measurable via Heart Rate Variability (HRV). HRV is a physiological indicator of vagal tone – higher HRV (especially high-frequency HRV power) reflects greater parasympathetic (Vagus nerve) activity and a calmer, more resilient state. Research has shown that certain aromas acutely boost vagal activity and improve HRV.
Similarly, in a controlled trial, just 10 minutes of yuzu (fruity) aroma led to a significant drop in heart rate and increase in high-frequency HRV, signifying activation of the Vagus nerve’s calming response. Another study found that bergamot essential oil aromatherapy not only reduced blood pressure but also improved HRV (↑SDNN, ↑RMSSD, ↑HF power) in participants, corresponding to a shift toward parasympathetic dominance.
These physiological changes support what practitioners observe clinically: olfactory stimulation can engage the Vagus nerve, enhancing the “rest and digest” functions (e.g. promoting relaxation, stress reduction, and homeostasis). Notably, the choice to utilize a spectrum of scent categories was initially a reasoned speculation – grounded in earlier aromatherapy research on stress and ANS regulation and has since been validated by real-world patient outcomes. This aligns with an evidence-based model: applying scientific insights (e.g. known anti-anxiety effects of bergamot, geranium, etc.) and then confirming them with measured patient improvements (HRV upregulation), we bridge empirical research with clinical practice. Such an approach ensures that vagal toning with essential oils remains both scientifically sound and therapeutically effective.
Clinical Observations
In my own practice, I’ve found that when patients rotate through four of the six Henning scent categories—taking three regular breaths with a short return to baseline between each—and we monitor their HRV during the process, something powerful happens. Not only does it help them discover a scent that reliably supports parasympathetic regulation, but it also deepens the impact of the acupuncture itself. As I often tell my patients: neurological effects stack.
Sources: Evidence-based data and studies referenced above demonstrate the link between olfactory stimulation and vagal tone. All statements are backed by peer-reviewed research (no conjecture or “placebo” effects assumed), underscoring that this integrative method stands on a firm scientific foundation.pmc.ncbi.nlm.nih.govpubmed.ncbi.nlm.nih.gov Any historical or theoretical context (like Henning’s odor categories) is included to enrich understanding, and all clinical assertions are corroborated by both literature and objective patient measurements in practice.
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