Regularity of Human Body Temperature Change Induced by Various Aromatic Smokes

Incense therapy (aromatherapy) is a natural treatment that stimulates the human respiratory system and skin through the natural volatilization or combustion of plants of some animal secretions [1]. It serves as a complementary therapy to help restore the body and mind to a state of balance [2]. However, the systematic mechanism of aromatherapy has seldom been investigated. Traditional Chinese medicine (TCM) posits that aromatherapy may interact with the human meridian [3]. The meridian system is a core component of TCM theory, mainly including the six normal meridian pairs and eight extra meridians, and may be related to the diversity of the transmembrane channels. These views provide a new hypothesis that is worth experimentation and systematic validation.

Transmembrane transportation consumes ATP and generates thermal infrared signals. Infrared thermography, a non-invasive imaging technique, has been progressively introduced into meridian research in recent years [4]. Previously, we successfully used infrared imageries to capture the thermal effects of tea activating the human meridian system. We discovered that after drinking different types of tea, the temperature in both the fingers and organs increased significantly. These temperature changes highly corresponded with the six normal meridian pairs [5].

This study uses natural fragrances as a model to investigate the thermal effects of incense smoke on the human body surface through combustion experiments and infrared thermography, and to determine whether it exhibits consistent, classifiable thermal imaging characteristics.

The 123 kinds of incense samples selected for the experiment were ground and sieved. Six members of our research group (aged 20–50) served as healthy volunteers (M0–M5). All 123 aromatic smokes were tested in each participant (n = 6 per aromatic smoke). During the experiment, participants were prohibited from consuming any medications, tea, or seasonings to avoid potential interference. Prior to imaging, participants sat quietly in a temperature-controlled room (26–28 °C) for 20 min to stabilize body temperature. Each incense sample (500 mg) was burned in a controlled setting, and thermal images of both ventral and dorsal sides were captured at 10 min of combustion. The infrared camera (Ti450PRO Thermal Imager, Fluke Co., Everett, WA, USA) was fixed three meters from the subject, capturing the head, upper limbs, and torso. To minimize interference, only one fragrance was tested per day.

The experiment showed that most natural fragrances induced a localized or systemic increase in temperature after 10 min of burning. Smoke of some fragrances, including Aquilaria sinensis, Santalum album, Osmanthus fragrans, Prunus mume f. alba, Ruta graveolens, Thuja sutchuenensis, Rosa rugosa, and Syzygium aromaticum, produced stable and significant surface warming patterns across multiple subjects (n = 6). These patterns were highly similar to the distribution pathways of the eight extra meridians (Figure 1).

Images derived from participant M0, illustrating typical warming patterns. The eight representative fragrances shown in Figure 1 are listed in Table 1 using the same Latin names.

The warming induced by lignaloo mainly descends from the face along the midline of the abdomen, consistent with the Gravidity meridian. Sandalwood induces warming in the coccygeal vertebra, along the spinal midline to the head, consistent with the Spine meridian. The warming area of osmanthus (Osmanthus fragrans) is distributed around 3cm lateral to the midline of the abdomen and ascends along the inner side of the spine to the neck, which is consistent with the distribution of the Spout meridian. Plum blossom (Prunus mume f. alba) causes a circumferential warming pattern around the waist, corresponding to the Belt meridian. The warming areas of the common rue leaves are concentrated around 7 cm lateral to the midline of the abdomen, chest, and cheeks, matching the Yim-teaser meridian. Thuja sutchuenensis or cedar primarily warms the hips, shoulders, and eyes, aligning with the Yang-teaser meridian. Rose induces warming in the sides of the abdomen and the upper neck region, corresponding to the Yim-binder meridian. Clove triggers warming in the whole back and abdomen, shoulders, neck, and back side of the head, consistent with the Yang-binder meridian.

Beyond the representative samples above, warming effects of other fragrances can be categorized into one of these eight thermal effect patterns through image comparison or exhibit overlapping patterns (Table 1).

This study was the first time to systematically observe and categorize thermal response patterns induced by natural incense smoke in the human body. Results showed that most incense types could be grouped into eight thermal patterns, which highly correspond with the eight extra meridians in TCM. This suggests that natural aromatherapy fragrances may induce localized temperature increases by acting on specific pathways, providing imaging-level observations that resemble classical meridian descriptions. Furthermore, molecules absorbed through the respiratory system trigger entirely different meridian effects from those absorbed through the digestive system, i.e., those through the respiratory system enter the eight extra meridians, while those through the digestive system enter the six normal meridian pairs. These observations further suggest that the traditional classification of TCM meridians may reflect underlying, yet currently undefined, principles of physiological organization, which warrant further systematic investigation.

Although the present study focuses only on the phenomenology of thermal patterns, the observed spatial heterogeneity in surface temperature responses may be contributed to by several biological factors. Regional differences in the types and density of sensory receptors [6,7], autonomic nerve innervation [8,9], microvascular distribution [10,11,12], and tissue metabolic activity could all influence how inhaled aromatic compounds modulate local heat dissipation. These factors may shape reproducible thermal configurations without implying discrete anatomical conduits. At present, such considerations remain speculative and serve primarily to outline biologically plausible contexts for future mechanistic investigations.

Infrared thermography is inherently sensitive to environmental and physiological fluctuations. In this study, reproducibility was evaluated not through absolute temperature values but through the recurrence of spatial thermal configurations across individuals exposed to identical fragrance types. While generalized autonomic responses, such as vasodilation induced by smoke inhalation, may contribute to global warming effects, they are unlikely to fully explain the consistent, pathway-like distributions repeatedly observed. This suggests that the thermal patterns reflect structured physiological responses rather than random or purely systemic effects.

Several limitations must be acknowledged. First, the number of participants was limited, limiting population-level generalization and precluding statistical modeling of inter-individual variability. The present classification emphasizes pattern recurrence rather than quantitative magnitude or prevalence. Second, correspondence between thermal patterns and the eight extra meridians should be interpreted as a conceptual analogy derived from TCM theory, rather than as evidence of discrete physiological structures. Terms such as “meridian-specific warming effects” are used descriptively to facilitate interdisciplinary dialogue, not to assert mechanistic equivalence.

In aromatherapy, the chemical composition and relative abundance of smoke constituents released during the combustion of natural incense are key factors influencing their physiological effects. Future studies should employ gas chromatography–mass spectrometry (GC–MS) to systematically characterize the chemical profiles of smoke derived from different natural incense materials. Comparative analysis of differential components may help elucidate common patterns underlying their physiological effects and potential molecular mechanisms. In parallel, expanding participant cohorts will facilitate quantitative assessment of inter-individual variability, response stability, and statistical robustness. Together, these approaches may help bridge phenomenological observations with molecular and physiological mechanisms.

Conceptualization, H.L.; Methodology, H.L. and W.J.; Software, W.J.; Validation, H.L., W.J. and L.Y.; Formal Analysis, M.W. and L.Y.; Investigation, L.Y. and X.B.; Resources, H.L. and L.Y.; Data Curation, M.W.; Writing—Original Draft Preparation, M.W.; Writing—Review & Editing, H.L.; Visualization, W.J.; Supervision, H.L.; Project Administration, H.L.; Funding Acquisition, H.L.

The study was conducted according to the guidelines of the Declaration of Helsinki, and approved by the Ethics Committee of Fudan University School of Life Sciences (BE1945, 18 December 2019).

Informed consent was obtained from all subjects involved in the study.

There are no additional data for this paper other than published in the manuscript.

This work was supported by National Key R&D Program of China (2020YFE0201600).

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.