Sandalwood (Santalum album L.): A Comprehensive Reference
1. Identity and Botanical Classification
1.1 Taxonomic and Chemical Identity
Santalum album L. (family Santalaceae), commonly known as Indian sandalwood, is one of the oldest and most precious sources of natural fragrance, with immense medicinal and commercial significance. It is also commonly known as white sandalwood or East Indian sandalwood. The primary commercial product — sandalwood oil, also called East Indian sandalwood oil (EISO) or sandalwood album oil (SAO) — is an essential oil distilled from the Santalum album tree.
Santalum album is an evergreen tree that grows between 4–9 metres. It is variable in habit, usually upright to sprawling, and may intertwine with other species. The plant parasitises the roots of other tree species, with a haustorium adaptation on its own roots, but without major detriment to its hosts. Up to 300 species (including its own) can host the tree's development, supplying macronutrients phosphorus, nitrogen and potassium, and shade, especially during early phases of development.
The central part of the tree — the heartwood — is the only part used for its fragrance. It is yellow-brown in color, hard with an oily texture, and due to its durability is a preferred material for carving. The outer part of the tree, the sapwood, is unscented. The absence of heartwood in young trees provides little reason for using trees under 20–25 years old for the production of oil. At around 30–50 years, the extent of heartwood formation is at its maximum.
1.2 Related Species and Standards
Worldwide, there are more than a dozen species of sandalwood, most of which have served as sources of essential oil. However, the International Organization for Standardization (ISO) has issued standards for only two species: Santalum album and Santalum spicatum (West Australian sandalwood). Of the two species, S. album produces oil with much higher concentrations of alpha- and beta-santalol.
Santalum album — native to Indonesia, India, Sri Lanka (possibly naturalised), and Timor-Leste — is the most highly regarded species in international commerce, traded as both heartwood and oil under East Indian sandalwood oil International Organization for Standardization (ISO) standard 3518:2002.
1.3 Conservation Status
Conservation efforts are crucial due to over-exploitation and declining natural populations; S. album is classified as vulnerable by the IUCN. Centuries of over-exploitation have led to the demise of sandalwood in natural stands, and large plantations are now being established throughout northern Australia to satisfy demand and conserve remaining reserves.
2. Common Forms and Preparations
Sandalwood is commercially available in several distinct forms, each with different applications:
- Essential oil (SAO/EISO): Sandalwood oil is an essential oil obtained from the steam distillation of chips and billets cut from the heartwood of various species of sandalwood trees, mainly Santalum album (Indian sandalwood) and Santalum spicatum (Australian sandalwood). Heartwood chips are distilled for 14–72 hours depending on the operation, yielding 4–6% essential oil.
- Heartwood powder: The dried, finely ground heartwood, used as a paste by mixing with water or carrier liquids, is one of the oldest and most widespread preparations in traditional medicine and ritual practice.
- Pharmaceutical-grade oil: Most commercially available sandalwood oils are poorly characterized and may contain residual solvents, adulterants, other essential oils, synthetic fragrances, and/or bulking or extending agents. Such materials are not generally manufactured and tested in accordance with the US FDA's 2004 Botanical Drug Development Guidelines and do not comply with the ISO specifications for EISO.
- Topical formulations: Clinical studies have employed preparations including creams, serums, and gels containing SAO at concentrations typically between 5% and 10% w/w.
- Incense and aromatherapy: Sandalwood oil has long been used as a noble perfume upon producing incense sticks, deodorants, cosmetics and aromatherapy agents as well as medicines.
- Food flavoring: Sandalwood oil is used in the food industry as a flavor ingredient, with a reported daily consumption of 0.0074 mg/kg.
3. Traditional and Historical Use
3.1 Ayurveda (India)
S. album has been cultivated in India for the last 25 centuries and esteemed all over the world for its sweet, long-lasting and medicinally valued fragrant oil. Sandalwood and the essential oil derived from sandal heartwood have been used in various traditional systems of medicine — including Ayurveda, Siddha, and Unani — in the treatment and prevention of a wide range of ailments.
In Ayurvedic texts, sandalwood carries the Sanskrit names Chandana and Srikhanda. The ancient Ayurvedic texts, including the Charaka Samhita and Sushruta Samhita, extensively document its therapeutic properties, especially its Dahaprashamana (relieves burning sensation) and Varnya (improves complexion) effects. In Ayurveda, the sandalwood plant is used as an expectorant, diuretic, astringent, stimulant, coolant, and sedative agent.
In Ayurvedic medicine, sandalwood is used to address conditions such as bleeding piles, vomiting, poisoning, hiccoughs, diarrhoea with bleeding, intrinsic haemorrhage, urticaria, inflammation of the umbilicus, and eye infections. For centuries, sandalwood was also used in traditional Ayurvedic medicine for ailments including colds, liver and gallbladder disease, hemorrhoids, urinary tract infections, muscle problems, and scabies.
In Ayurveda, sandalwood is classified as a cooling herb, making it essential for balancing the fiery Pitta dosha. Chandana paste is also an integral part of Hindu rituals, applied as a tilak on the forehead to cool the Ajna Chakra (third eye) and promote meditative focus.
3.2 Unani Medicine
Sandalwood and the essential oil derived from sandal heartwood have been used in the Unani system of medicine in the treatment and prevention of a wide range of ailments. In medieval Islamic and Unani traditions, by the 14th century, Mughal herbalists introduced sandalwood-infused attars (floral waters) for both fragrance and fevers.
3.3 Traditional Chinese Medicine and Other Traditions
Sandalwood album oil has been utilized topically for centuries in both Ayurvedic and traditional Chinese medicine. Across Southeast Asian cultures, sandalwood paste and oil have been applied to the skin for cooling, anti-inflammatory, and ritual purification purposes. The history of Indian sandalwood can be traced back over 4,000 years, where its essence was intricately woven into the spiritual, medicinal, and cultural practices of India. In ancient Hindu texts, sandalwood is often referred to as "chandan," a sacred material associated with purity, healing, and divinity.
3.4 European and Colonial-Era Trade
European traders prized sandalwood woodchips and oil, exporting them to colonial apothecaries where they were adapted into tonics, tooth powders, and soaps. The first commercial extraction of its essential oil occurred in Mysore, India, in 1917. For many years, the oils were then further processed in the perfumeries at Grasse, France.
4. Key Constituents and Active Compounds
4.1 Sesquiterpene Alcohols (Primary Constituents)
Approximately 90% of S. album essential oil is composed of the sesquiterpene alcohols α-, β-, and epi-β-santalol and α-exo-bergamotol. The current International Organization for Standardization (ISO) standards for S. album oil are 41–55% α-santalol and 16–24% β-santalol (ISO 3518: 2002E).
The oil is distilled from the heartwood of the Santalum album tree and contains over 125 structurally related compounds, with fewer than a dozen components present in concentrations greater than 1% by weight.
The primary biologically active compounds include:
- α-Santalol (alpha-santalol): A naturally occurring sesquiterpene derived from sandalwood oil. It is the most pharmacologically studied constituent and the primary driver of documented biological activities.
- β-Santalol (beta-santalol): The α- and β-santalols are the most important contributors to sandalwood oil fragrance.
- Additional sesquiterpenoids: Sandalwood oil additionally includes α-santalene, β-santalene, α-bergamotene, epi-β-santalene, β-bisabolene, α-curcumene, β-curcumene, and γ-curcumene.
- Lanceol and α-bisabolol: Lanceol and α-bisabolol are also found in modest concentrations.
Phytochemical evaluation also reveals that the tree is rich in terpenoids, saponins, phenolics, and tannins. In seeds of Santalum album, there is a compound known as santalbic acid, which has antibacterial properties against gram-positive bacteria and antifungal effects on many types of pathogenic fungi.
4.2 Biosynthesis of the Santalols
The enzyme SaCYP736A167 has been characterized as a multi-substrate cytochrome P450, which stereo-selectively produces (Z)-α-santalol, (Z)-β-santalol, (Z)-epi-β-santalol and (Z)-α-exo-bergamotol, matching the composition of authentic sandalwood oil. This work completes the discovery of the biosynthetic enzymes of key components of sandalwood fragrance, and highlights the evolutionary diversification of stereo-selective P450s in sesquiterpenoid biosynthesis.
5. Mechanisms of Action
5.1 Anti-inflammatory Mechanisms
East Indian sandalwood oil (EISO) directly inhibited phosphodiesterase (PDE) enzymatic activity in vitro. In lipopolysaccharide-stimulated human dermal fibroblast, BEAS-2B, A549, and THP-1 cells, EISO suppressed total cellular PDE activity, PDE4 and 7 transcript levels, nuclear factor kappa B (NF-κB) activation, and pro-inflammatory cytokines/chemokine production. PDE4 is overactive in chronic relapsing inflammatory skin diseases such as psoriasis and eczema/atopic dermatitis, and in several cancers.
The wide range of health benefits of alpha-santalol have been attributed to the modulation of various signalling pathways involved in the development of particular diseases. The antitumour and cancer preventive properties of alpha-santalol have been shown to involve cell death induction through apoptosis and cell cycle arrest in various cancer models. A marked decrease in inflammatory markers has also been shown with alpha-santalol administration in skin tissue models.
5.2 Anticancer and Chemopreventive Mechanisms
Alpha-santalol's ability to induce cell-cycle arrest and apoptosis in cancer cells is its most reported anticancer mechanism of action. Specifically, alpha-santalol at 50–100 µM decreased cell viability from 24 hours of treatment, and alpha-santalol at 50–75 µM induced G2/M phase cell cycle arrest from 6 hours of treatment in both A431 (human epidermoid carcinoma) and UACC-62 (human melanoma) cells. Alpha-santalol altered expressions of cell cycle proteins such as cyclin A, cyclin B1, Cdc2, Cdc25c, p-Cdc25c, and Cdk2 — all critical for G2/M transition.
Results from UVB irradiation studies suggest that alpha-santalol prevents skin cancer development by inducing proapoptotic proteins via an extrinsic pathway and increasing p53.
5.3 Olfactory Receptor Activation and Wound Healing
The olfactory receptor OR2AT4 is expressed in keratinocytes and has been shown to bind to sandalwood odorants, resulting in elevation of intracellular calcium levels and phosphorylation of extracellular kinases (Erk1/2) and p38 mitogen-activated kinases, promoting keratinocyte proliferation and wound healing in human skin ex vivo. It has been postulated that OR2AT4, or a similar receptor, may also be activated by α-santalol.
5.4 Antifungal Mechanisms
Based on morphological changes in immobilized Trichophyton hyphae, the inhibitory effect of α-santalol on mitosis was assessed using sea urchin embryos; α-santalol was revealed to be a potent antimitotic agent by interference with microtubule assembly — a mechanism analogous to the antifungal drug griseofulvin.
5.5 Neurological and Psychophysiological Effects
In mice, the most active sedative constituents in a Santalum album extract were α-santalol and β-santalol. In rat brain, sandalwood oil was a potent antagonist of dopamine and serotonin receptor binding, suggesting an antipsychotic, tranquillizing effect. It was also significantly analgesic, and inhibited δ-2 opioid receptors.
5.6 Tyrosinase Inhibition
Alpha-santalol was found to be an inhibitor of tyrosinase, a key enzyme in the biosynthetic pathway for the skin pigment melanin. This intriguing finding suggests that SAO may potentially act as an inhibitor of abnormal pigmentation associated with aging and exposure to ultraviolet light.
6. Scientific Evidence by Area of Use
6.1 Dermatology: Acne
Evidence level: Preliminary clinical (uncontrolled trial)
Potential anti-inflammatory action of sandalwood oil was shown in a clinical trial of sandalwood oil-containing treatment regimen for eight weeks in 50 patients with mild to moderate facial acne. Treatment was well tolerated by nearly all patients, and 89% of patients showed improvement in their disease, with notable reductions in lesion counts in patients with more severe or inflamed lesions. This was an open-label, uncontrolled trial, limiting the ability to draw definitive conclusions about efficacy compared to placebo.
6.2 Dermatology: Psoriasis and Atopic Dermatitis
Evidence level: Early-phase clinical trials (open-label and Phase 2)
In one study, 75% of pediatric eczema/atopic dermatitis patients treated with topical EISO formulations achieved a >50% reduction in their Eczema Area and Severity Index (EASI) score. EISO treatment of a psoriasis model also reduced PDE4 expression and reversed histopathology.
A single-center, open-label safety, tolerability, and efficacy trial of an anhydrous serum formulation of EISO at a dose level of 10% w/w EISO (in a caprylic/capric triglyceride, dimethyl isosorbide, ethoxydiglycol formulation) was conducted for the treatment of mild to moderate plaque psoriasis in adult subjects. The study enrolled 12 subjects over 18 years old, each with a maximum of 10% body surface area affected by plaque psoriasis.
A further double-blind, randomized, placebo-controlled trial evaluated SAN007 (5% East Indian sandalwood oil in a cream formulation) when administered daily for up to 28 days to patients at least 18 years of age with atopic dermatitis. All enrolled subjects received either 5% SAN007 cream or placebo cream (randomized in a 2:1 ratio) or 10% SAN007 cream or placebo cream (randomized in a 2:1 ratio).
Data from initial proof-of-concept clinical studies in acne, warts, molluscum contagiosum, atopic dermatitis, and psoriasis indicate that SAO is safe, well-tolerated, and has potential for broader use as a novel botanical therapeutic. However, the existing trials are generally small in sample size and many lack robust placebo-controlled designs, meaning results must be interpreted with caution.
6.3 Dermatology: Common Warts and Molluscum Contagiosum
Evidence level: Patented and registered use; Phase 2 trials ongoing/completed
Pediatric clinical studies examining SAO in the treatment of human papillomavirus (HPV) warts or molluscum contagiosum led to the issuance of three United States patents related to the use of sandalwood album oil for the treatment of these skin conditions. Several on-going and completed clinical trials studying SAO are listed on clinicaltrials.gov in a variety of indications, including verruca vulgaris (common warts), molluscum contagiosum, genital warts, psoriasis, oral mucositis, and atopic dermatitis.
6.4 Skin Cancer Chemoprevention
Evidence level: Preclinical (animal and cell-line); no completed human trials
Cell line and animal studies have reported chemopreventive effects of sandalwood oil and α-santalol without causing toxic side-effects. These anticancer effects were identified in chemically-induced skin carcinogenesis in CD-1 and SENCAR mice, ultraviolet-B-induced skin carcinogenesis in SKH-1 mice, and in vitro models of melanoma, non-melanoma, breast and prostate cancer.
Studies have indicated skin cancer chemopreventive effects of sandalwood oil in CD-1 mice. The purpose of one specific investigation was to study the skin cancer chemopreventive effects of alpha-santalol, a principal component of sandalwood oil, in CD-1 and SENCAR mice. Additional experimental and clinical studies are needed to investigate the chemopreventive effect of alpha-santalol in skin cancer in humans.
6.5 Radiation-Induced Dermatitis
Evidence level: Single clinical study
Topical application of sandalwood oil and turmeric-based cream was found to effectively prevent radiation-induced dermatitis in patients receiving chemotherapy radiation. This finding comes from a single study and requires replication in larger, controlled trials.
6.6 Antimicrobial Activity
Evidence level: In vitro and limited in vivo; no large human clinical trials specifically for infections
Antimicrobial activity of leaf and stem aqueous extracts of Santalum album was observed against Escherichia coli, Staphylococcus aureus, and Pseudomonas. In another study, the antibacterial activity of the aqueous extract was evaluated against strains of Escherichia coli, Klebsiella pneumoniae, Klebsiella oxytoca, Pseudomonas aeruginosa, Staphylococcus aureus, Bacillus subtilis, and Aeromonas species. It showed strongest inhibitory activity of 87% against Staphylococcus aureus, while inhibition of other tested strains ranged between 66% and 78%.
Minimum inhibitory concentration (MIC) for sandalwood oil was determined to be in the range of 0.078–5 µg/ml for most of the test micro-organisms screened.
α-Santalol and β-santalol both showed significant antifungal effect against the dermatophytic fungus Trichophyton rubrum. Crude organic fractions and sesquiterpenoids from sandalwood oil also demonstrated antimicrobial activity against Helicobacter pylori, which causes peptic ulcers and may contribute to gastric cancer. These are laboratory findings; there are no large-scale human clinical trials specifically validating sandalwood as a stand-alone antimicrobial treatment in infectious disease.
6.7 Antiviral Activity
Evidence level: In vitro only
Sandalwood oil had in vitro antiviral activity against Herpes simplex virus (HSV)-1 and HSV-2. It inhibits viral replication in a dose-dependent manner and is more effective against HSV-1. These findings are preliminary and have not been confirmed in human clinical trials.
6.8 Anxiety and Psychophysiological Effects
Evidence level: Preclinical and small human physiological studies
A human physiological study examined the effects of SAO and isolated alpha-santalol on physiological parameters after transdermal absorption. The study investigated the effects of East Indian sandalwood oil and alpha-santalol on physiological parameters as well as on mental and emotional conditions in healthy human subjects after transdermal absorption. To exclude olfactory stimulation, inhalation of the fragrances was prevented by breathing masks. Eight physiological parameters — including blood oxygen saturation, blood pressure, breathing rate, eye-blink rate, pulse rate, skin conductance, skin temperature, and surface electromyogram — were recorded. Subjective mental and emotional condition was assessed by means of rating scales. While alpha-santalol caused significant physiological changes interpreted in terms of a relaxing/sedative effect, sandalwood oil provoked physiological deactivation but behavioral activation. These results are from small-sample physiological studies and are not yet supported by large randomized controlled clinical trials.
6.9 Wound Healing
Evidence level: In vitro and ex vivo mechanistic evidence
A publication presented data showing that, in cultured keratinocytes, SAO enhanced expression of transcription factors (snail, twist) and mesenchymal factor (vimentin), all of which are related to the epithelial-mesenchymal transition (EMT) — a process involved in wound healing and tissue repair. Album oil also promoted epidermal wound healing in vivo compared to vehicle control. Human clinical evidence for wound healing specifically remains limited.
7. Body Systems and Health Areas of Association
- Integumentary (skin): The most evidence-supported area of use. Sandalwood album oil has shown promise in clinical trials for treatment of acne, psoriasis, eczema, common warts, and molluscum contagiosum.
- Immune/inflammatory: Pre-clinical and clinical studies have shown the role of sandalwood extract as antioxidant and anti-inflammatory.
- Central nervous system: In mice, α-santalol and β-santalol were identified as the most active sedative constituents. In rat brain, sandalwood oil acted as a potent antagonist of dopamine and serotonin receptor binding, suggesting an antipsychotic, tranquillizing effect.
- Antimicrobial (skin and mucosa): Laboratory evidence supports antibacterial and antifungal activity; pre-clinical studies have shown antibacterial, antifungal, and antiviral roles for sandalwood extracts.
- Oncology (preclinical): α-Santalol, a sesquiterpene isolated from sandalwood, is known for anti-inflammatory, anti-oxidant, anti-viral and anti-bacterial activities, and cell line and animal studies have reported chemopreventive effects of sandalwood oil and α-santalol without causing toxic side-effects.
- Urinary tract (traditional): Sandalwood has been traditionally used in various cultures, particularly in Ayurvedic medicine, for supportive treatments related to urinary tract infections.
- Gastrointestinal (traditional): Traditional use has also encompassed digestive issues.
8. Dosage Forms and Reported Dosages
The following dosages are reported specifically in source materials and clinical study protocols:
- Acne (topical, open-label clinical trial): Sandalwood oil-containing treatment regimen was administered for eight weeks in 50 patients with mild to moderate facial acne, with the treatment well tolerated by nearly all patients. The specific concentration used in this formulation is not specified in available review sources.
- Atopic dermatitis (topical, randomized controlled trial): SAN007 formulated at 5% East Indian sandalwood oil in a cream formulation was administered daily for up to 28 days. An arm using 10% SAN007 cream was also included, randomized against placebo in a 2:1 ratio.
- Psoriasis (topical, open-label trial): A 10% w/w EISO in a caprylic/capric triglyceride, dimethyl isosorbide, ethoxydiglycol formulation was evaluated in a single-center open-label trial.
- Cell line studies (α-santalol): α-Santalol at 50–100 µM decreased cell viability in cancer cell lines from 24 hours of treatment, and at 50–75 µM induced G2/M phase cell cycle arrest from 6 hours of treatment.
- Antibacterial MIC: MIC for sandalwood oil was determined to be in the range of 0.078–5 µg/ml for most test micro-organisms screened.
- Food industry use: Sandalwood oil is used as a flavor ingredient in the food industry at a reported daily consumption of 0.0074 mg/kg.
9. Safety Considerations and Interactions
9.1 General Toxicity Profile
No significant toxicity has been indicated by sandalwood oil or its individual constituents. Sandalwood oil and its major constituent have low acute oral and dermal toxicity in laboratory animals. Although the available information on toxicity of sandalwood oil is limited, it has a long history of oral use without reported adverse effects and is considered safe at present use levels.
The dermal LD50 in rats is in excess of 5 g/kg of body weight. When applied to human subjects in patch testing, neither neat sandalwood oil nor a 10% SAO ointment produced irritation or sensitization.
9.2 Allergic Contact Sensitization
The European Union Scientific Committee on Consumer Safety (SCCS) has categorised Australian sandalwood oil as an "established contact allergen in humans," based on the content of well-known allergenic compounds (santalols). Many clinical studies are available on the skin sensitisation of santalol in humans. In diagnostic patch tests, positive results were observed with incidences of 0.0071–1.53% when santalol was tested at up to 10% concentration. However, no sensitisation was observed at 20% concentration in 25 male volunteers in a human maximisation test. In a 6-year patch test study, patients with facial dermatoses were tested with a mixture of alpha and beta-santalol at up to 10% concentration and positive reactions were seen at an incidence of 1.5%.
Occasional cases of irritation or sensitization reactions to sandalwood oil in humans are reported in the literature.
9.3 Adulteration and Quality Concerns
Most commercially available sandalwood oils are poorly characterized and may be of low grade, often containing residual solvents, adulterants, other essential oils, synthetic fragrances, and/or bulking or extending agents. Oil yield, fragrance profile, and quality depend heavily on tree age, heartwood quality, species genetics, and the extraction and purification methodology. This is a practical safety concern because studies demonstrating efficacy and tolerability were conducted using pharmaceutical-grade, ISO-compliant material.
9.4 Potential Drug and Receptor Interactions
In rat brain studies, sandalwood oil acted as a potent antagonist of dopamine and serotonin receptor binding, and inhibited δ-2 opioid receptors. These findings in animal models suggest the theoretical possibility of pharmacodynamic interactions with sedative medications, antipsychotics, or opioid-based drugs; however, clinical data confirming these interactions in humans is not established in the available literature.
9.5 GRAS Status
Sandalwood oil was not mutagenic in the spore Rec assay and was found to have anticarcinogenic, antiviral, and bactericidal activity. Sandalwood oil has historically been used as a food flavoring ingredient and carries a GRAS (Generally Recognized As Safe) designation in the United States for flavoring purposes at low consumption levels.
9.6 ISO Compliance and Product Integrity
The ISO standard for the accepted characteristics of East Indian sandalwood essential oil is ISO 3518:2002. This standard specifies that S. album oil must contain 41–55% α-santalol and 16–24% β-santalol. Products that do not meet these specifications may have substantially different biological activity profiles from those studied in published research.
10. Summary of Evidence Strength
The overall body of evidence for sandalwood and its isolated constituents varies substantially by application:
- Topical dermatological use (acne, eczema, psoriasis, warts): The strongest human evidence exists here, with multiple small proof-of-concept and Phase 2 trials yielding favorable safety and tolerability data, and preliminary efficacy signals. The favorable safety profile, ease of topical use, and recent availability of pharmaceutical-grade sandalwood album oil support its broader use as the basis of novel therapies in dermatology, but larger, well-controlled trials are needed.
- Skin cancer chemoprevention: Evidence is preclinical (cell lines and multiple animal models) and promising, but additional experimental and clinical studies are needed to investigate the chemopreventive effect of alpha-santalol in skin cancer in humans.
- Antimicrobial/antiviral activity: Demonstrated in vitro; clinical translation in humans has not been systematically evaluated in controlled trials.
- Anxiolytic/CNS effects: Animal model data and small human physiological studies support a relaxing/sedative effect, but robust randomized clinical trial data in human subjects are lacking.
- Traditional uses (urinary, gastrointestinal, fever): These uses are well-documented historically across multiple systems of medicine but lack modern controlled clinical evidence.
References
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