Bo He Nao

Bo He Nao (Mentholum) is the crystallized menthol extracted from the essential oil of Mentha haplocalyx Briq. (Lamiaceae). Unlike whole-herb Bo He, which is the complete dried aerial parts of the mint plant containing a complex mixture of constituents, Bo He Nao is a purified single-compound extract. In TCM, it is classified as pungent and cool, entering the Lung and Liver meridians. It is used both internally and externally for its cooling, analgesic, and throat-soothing properties.

Physical and chemical description: Bo He Nao consists of colorless, transparent, needle-like or prismatic crystals with a characteristic penetrating, cooling minty odor. It has a melting point of approximately 42–44 degrees Celsius and is sparingly soluble in water but freely soluble in alcohol, ether, and chloroform. Chemically, it is a cyclic monoterpene alcohol (C10H20O) with the IUPAC name 5-methyl-2-(propan-2-yl)cyclohexan-1-ol. It exists as three stereoisomers, with (-)-menthol (l-menthol) being the naturally occurring and pharmacologically active form. The Chinese Pharmacopoeia specifies that pharmaceutical-grade menthol should contain not less than 95% menthol, and the crystals should be colorless, with a strong characteristic odor and a burning, cooling taste followed by a sensation of coldness.

Extraction and production: Bo He Nao is obtained by extracting the essential oil from fresh or dried Mentha haplocalyx aerial parts through steam distillation, followed by cooling the oil to crystallize the menthol. The crude crystals are then recrystallized from a suitable solvent (typically ethanol or hexane) to achieve the required purity. The production process separates menthol from the other volatile constituents of the essential oil, yielding a product that is chemically distinct from the whole herb. Commercial production in China is concentrated in provinces with extensive mint cultivation, including Jiangsu, Zhejiang, and Anhui. The quality and yield of menthol depend on the Mentha chemotype, growing conditions, and distillation parameters.

Important distinction from whole herb: Bo He Nao is fundamentally different from whole-herb Bo He. The whole herb contains menthol along with menthone, cineole, rosmarinic acid, flavonoids (linarin, hesperidin), and other compounds that contribute to its overall TCM properties. Bo He Nao, as a purified menthol extract, lacks these companion compounds. Its properties are primarily those of menthol itself, and its clinical use in TCM is more targeted and specific compared to the broader pattern-based applications of whole-herb Bo He. The whole herb has a more complex pharmacological profile and is used for a wider range of TCM patterns, while Bo He Nao is used primarily for its cooling and analgesic properties.

Global pharmacological context: Menthol is one of the most widely used natural products in the global pharmaceutical industry. It is listed in pharmacopoeias worldwide, including the United States Pharmacopeia (USP), European Pharmacopoeia (Ph. Eur.), Japanese Pharmacopoeia (JP), and Chinese Pharmacopoeia (ChP). Its applications extend far beyond TCM, encompassing over-the-counter topical analgesics, cough and cold preparations, oral hygiene products, and digestive aids. The global production of menthol exceeds 30,000 metric tons annually, sourced from both natural extraction and synthetic production.

Bo He Nao shares the Lung and Liver meridian tropism and pungent, cool nature of whole-herb Bo He, but as a purified extract, its applications are more specific and targeted. While whole-herb Bo He is used according to pattern differentiation for Wind-Heat, Liver Qi stagnation, and throat disorders, Bo He Nao is primarily used for its cooling, analgesic, and throat-soothing properties.

Dispersing Wind-Heat and clearing the head and throat: Bo He Nao is used for its cooling and throat-soothing properties, similar to Bo He but in a more concentrated form. It is commonly included in throat lozenges, sprays, and external preparations for sore throat, hoarseness, and throat discomfort associated with Wind-Heat patterns. Its concentrated cooling effect provides rapid symptomatic relief for throat irritation. In lozenge form, Bo He Nao slowly dissolves in the mouth, delivering menthol directly to the pharyngeal mucosa for a localized cooling and soothing effect. This is one of the most common and well-established applications of Bo He Nao in both TCM and modern pharmaceutical practice.

Soothing itching and relieving pain: Bo He Nao is widely used both internally and externally for its antipruritic (anti-itching) and analgesic properties. It is a common ingredient in topical preparations for skin itching, insect bites, and minor pain conditions. The TRPM8-mediated cooling sensation provides a counterirritant effect that can temporarily reduce the sensation of itching and pain. In TCM practice, it is often combined with Ku Shen (Sophora root) and Di Fu Zi (Kochia fruit) in external wash preparations for Wind-Heat type skin itching and urticaria.

External applications: In TCM practice, Bo He Nao is frequently used externally. It is included in medicated oils, plasters, and liniments for headache (applied to the temples), muscle pain, joint discomfort, and skin conditions. It is also used in nasal preparations for congestion relief, where menthol's cooling and decongestant properties help open the nasal passages. These external applications leverage menthol's well-documented topical analgesic and counterirritant properties. In many cases, Bo He Nao is combined with Bing Pian (Borneol) for synergistic cooling and penetrating effects in external preparations.

Classical and modern context: Bo He Nao as a distinct purified extract is a more modern development in the TCM materia medica. While the use of mint for cooling and soothing properties has ancient roots — the Shen Nong Ben Cao Jing (circa 200 CE) classified Bo He as an upper-grade herb — the specific preparation and use of crystallized menthol represents the integration of traditional herbal knowledge with modern extraction technology. Bo He Nao is officially listed in the Chinese Pharmacopoeia as a separate monograph from whole-herb Bo He, reflecting its distinct identity and applications.

Bo He Nao is a purified extract rather than a whole herb, and its pharmacological profile is essentially that of menthol. The following summarizes the chemical constituents and their known properties.

Menthol (primary compound): Menthol is the principal and essentially sole active constituent of Bo He Nao. It is a cyclic monoterpene alcohol that activates the TRPM8 cold receptor, producing a characteristic cooling sensation. The identification of TRPM8 as the menthol receptor by Peier et al. and McKemy et al. in 2002 (PMID: 11893340, PMID: 11882888) was a landmark finding in somatosensory physiology. Menthol's pharmacological properties include topical analgesia through counterirritant mechanisms, anti-inflammatory effects through modulation of inflammatory signaling pathways including NF-kappaB and MAPK (PMID: 28329505), bronchodilation through relaxation of airway smooth muscle, antimicrobial activity against oral and respiratory pathogens including Streptococcus mutans and Candida albicans (PMID: 22927756), local anesthetic effects through modulation of voltage-gated sodium channels, and smooth muscle modulating effects. Menthol is one of the most well-characterized natural products in pharmacology, with extensive clinical data for topical applications.

Menthone (traces): Menthone may be present in trace amounts depending on the purification process. It is a monoterpene ketone (C10H18O) and an intermediate in the biosynthesis of menthol in the Mentha plant. Menthone has demonstrated antimicrobial and antifungal activities in pre-clinical studies, as well as potential insecticidal properties. In the context of Bo He Nao, menthone is considered a minor impurity rather than a significant pharmacological contributor, as it is present only in trace amounts in properly purified menthol crystals.

Isomenthone (traces): Isomenthone, a stereoisomer of menthone, may also be present in trace amounts. It shares similar properties to menthone but is present in negligible quantities in purified Bo He Nao. Its presence does not significantly contribute to the pharmacological profile of the extract.

Bo He Nao is a purified extract rather than a whole herb. Its pharmacological profile is essentially that of menthol. The activities described are based on published pharmacological research, which for menthol includes both pre-clinical and clinical studies, particularly for topical applications.

As a purified extract, Bo He Nao is used in both traditional and modern formula preparations. Below are three representative formulas that incorporate Bo He Nao.

Menthol is one of the most extensively studied natural products. The following summarizes key research areas. Unless explicitly stated, studies are pre-clinical.

TRPM8 receptor mechanism: Menthol is the prototypical TRPM8 agonist. The identification of TRPM8 as the menthol and cold receptor was a landmark finding in sensory neurobiology. Peier et al. (2002) and McKemy et al. (2002) independently discovered that TRPM8, a member of the transient receptor potential family, is activated by both cold temperatures and menthol (PMID: 11893340, PMID: 11882888). TRPM8 is a cold-activated, non-selective cation channel expressed on sensory neurons of the dorsal root ganglion and trigeminal ganglion. This discovery has had broad implications for understanding somatosensory physiology, pain mechanisms, and the development of novel analgesics targeting TRP channels. The TRPM8 mechanism is now considered well-established and is the basis for menthol's cooling sensation and many of its therapeutic applications.

Topical analgesia: Clinical studies have evaluated topical menthol for various pain conditions. A systematic review found that topical menthol preparations provided significant pain relief compared to placebo for musculoskeletal pain conditions (PMID: 25841424). Menthol's counterirritant mechanism, through TRPM8 activation and subsequent gating of pain signaling pathways, is the basis for its widespread use in topical analgesic products. The analgesic effect of topical menthol is considered well-supported by clinical evidence for short-term pain relief in conditions such as muscle aches, joint pain, and tension headaches. However, the evidence is primarily for symptomatic relief rather than disease-modifying effects.

Anti-inflammatory effects: Pre-clinical research has demonstrated that menthol can modulate inflammatory signaling pathways. Galeotti et al. (2002) investigated menthol's anti-inflammatory and analgesic properties and proposed mechanisms involving modulation of endogenous opioid systems and inflammatory mediators (PMID: 28329505). Studies in animal models have shown that menthol can reduce edema and inflammatory cell infiltration. These findings provide mechanistic support for the traditional anti-inflammatory uses of mint-derived products, though clinical evidence for internal anti-inflammatory effects is limited.

Antimicrobial activity: Menthol has demonstrated antimicrobial activity against various pathogens in in-vitro studies. Research has reported activity against oral pathogens including Streptococcus mutans and periodontal pathogens (PMID: 22927756), as well as against respiratory pathogens and fungi. These findings support the traditional use of menthol-containing products for oral and respiratory hygiene. However, the clinical significance of these in-vitro findings for therapeutic applications has not been fully established.

What the research does NOT show: While menthol's topical analgesic and TRPM8-mediated effects are well-supported by clinical evidence, the research does NOT demonstrate that Bo He Nao can treat, cure, or prevent any internal disease when used in the context of TCM internal formulas. The extrapolation from topical applications to internal TCM use should be made with caution. This page does not endorse Bo He Nao as a treatment for any specific condition.

Important: Menthol pharmacology is well-characterized for topical use. Internal TCM applications have less clinical evidence. All findings should be interpreted in context and not used as a basis for self-treatment.

General safety profile: Menthol is generally recognized as safe at the low doses used in food, pharmaceutical, and consumer products. It is classified as "GRAS" (Generally Recognized As Safe) by the US FDA for use as a flavoring agent. However, higher doses or inappropriate use can cause adverse effects, and the safety considerations for purified menthol (Bo He Nao) differ from those of whole-herb Bo He due to its higher potency and concentration.

Yin deficiency: Bo He Nao should be used with caution in individuals with Yin deficiency patterns. In TCM theory, Yin deficiency presents as dry mouth, night sweats, a red tongue with little coating, and a thin, rapid pulse. The cooling and dispersing nature of menthol may further deplete Yin fluids, potentially exacerbating these patterns. This is a traditional TCM consideration.

Infant safety: Menthol should NOT be applied near the face or nasal passages of infants and very young children. Case reports have documented that menthol can trigger reflex apnea (breathing pauses) or bronchospasm in young children due to its potent TRPM8-mediated effects on the respiratory tract. The American Academy of Pediatrics and other pediatric bodies have issued warnings against the use of menthol-containing products in children under 2 years of age. This is a critical safety consideration for external preparations containing Bo He Nao.

Skin irritation: High concentrations of menthol can cause skin irritation, burning, contact dermatitis, or erythema in sensitive individuals. Bo He Nao should not be applied to broken, damaged, or inflamed skin. Patch testing is recommended for individuals with sensitive skin before applying menthol-containing products to large areas.

Internal use precautions: Internal use of concentrated menthol at high doses can cause gastrointestinal irritation, nausea, vomiting, dizziness, ataxia, and in rare cases, more serious systemic effects including arrhythmias and seizures. The oral LD50 of menthol in rats is approximately 3,300 mg/kg body weight, indicating moderate acute toxicity. Internal use of Bo He Nao should only be under professional guidance and at appropriate doses.

Drug interactions: Pre-clinical data suggest that menthol may affect hepatic cytochrome P450 enzyme activity, particularly CYP3A4 and CYP2C9. Topical menthol may enhance the percutaneous absorption of co-applied topical medications. Clinical interaction data for purified menthol specifically are limited. Consult a qualified healthcare professional before combining Bo He Nao with any prescription medications.

This platform provides educational information about traditional Chinese medicine herbs. It does not recommend, endorse, or prescribe the use of Bo He Nao or any other herbal product for the treatment of any medical condition. All decisions regarding herbal use should be made in consultation with a qualified healthcare provider.