Styrax Tonkinesis Oil Loban (Styrax Tonkinesis)

Key constituents

Benzyl benzoate  51.7%

Benzyl alcohol 44.8%

(Z)-Cinnamyl (E)-cinnamate  2.1%

Cinnamic acid  1.8%

Ethyl cinnamate  1.1%

Benzoic acid  0.2%

Siam benzoin volatile compounds

Benzyl benzoate  38.9%

Benzyl alcohol  37.10%

Benzoic acid  19.1%

Ethyl cinnamate  0.7%

Quality

Benzoin resinoid is a sticky solid. To render it pourable, it is diluted to 50% in benzyl alcohol, benzyl benzoate, dipropylene glycol, or other solvent. Diethyl phthalate is less commonly used today as a diluent due to toxicity concerns (Burfield 2000). Small amounts of benzoic acid, benzyl cinnamate, ethyl cinnamate and vanillin may be added as odorous adulterants

Safety summary

Hazards  Skin sensitization (low risk).

Cautions (dermal)  Hypersensitive, diseased or damaged skin,

children under 2 years of age.

Maximum adult daily oral dose  368 mg

Maximum dermal use level  2%

Our safety advice

Our oral maximum is based on a limit of 5 mg/kg for ‘benzoic acid equivalents’, which constitute up to 95% of benzoin. Our dermal maximum is a best-practice estimate for skin safety.

Regulatory guidelines

A group ADI of 0–5 mg/kg body weight for benzoic acid, the benzoate salts (calcium, potassium and sodium), benzaldehyde, benzyl acetate, benzyl alcohol and benzyl benzoate, expressed as benzoic acid equivalents, was established by JECFA in 1996. The CIR Expert Panel considers that benzoic acid is safe to use in cosmetic formulations at concentrations up to 5%.

Organ-specific effects

Adverse skin reactions: In a modified Draize procedure on guinea pigs, benzoin ‘oil’ was skin sensitizing when used at 10% in the challenge phase (Sharp 1978). Benzoic acid and cinnamic acid have produced some allergic reactions. Benzyl benzoate and benzyl alcohol are listed in the EU as allergens, but the risk of allergy from either is negligible. In patch tests of 477 dermatitis patients, 45 (9.2%) had a positive
reaction to compound tincture of benzoin. Of the 45, 14 had strong positive reactions, and 28 had cross-reactions to similar allergens. Up to 80% of patients sentitive to Peru balsam reacted positively to Siamese benzoin. Since both raw materials contain coniferyl benzoate this may be responsible, but it is not known to be present in benzoin resinoids.

Reproductive toxicity  The reproductive toxicity data for benzyl benzoate, benzyl alcohol, benzoic acid and cinnamic acid do not suggest any restrictions in the use of benzoin
resinoid in pregnancy beyond those outlined above.

Systemic effects

Acute toxicity: No information found for benzoin. Benzyl alcohol and benzyl benzoate possess low acute toxicity. Carcinogenic/anticarcinogenic potential: Gum benzoin was
mutagenic in a mouse lymphoma assay (MLA), but not in Chinese hamster ovary cells. Gum benzoin produced CA in Chinese hamster lung cells, but was not genotoxic in a mouse micronucleus test or in the S. typhimurium TA135/pSK1002 umu test. It was not carcinogenic when fed to male rats at 125 or 250 ppm, to female rats at 250 or 500 ppm, and to male and female mice at 2,500 or 5,000 ppm for 104 weeks (National Toxicology Program 1980). The resinoid contains no known carcinogens, and the MLA and CHL results are false positives.

Comments

Analysis of the Tonkinesis compounds reveals little significant difference between the two types of benzoin, except for benzoic acid. Coniferyl benzoate, a non-volatile constituent of the raw gum (up to 75%), may contribute slightly to skin sensitization in some preparations of benzoin. Resinoids, and occasionally absolutes, are used in aromatherapy, though neither is soluble in fixed oil. There is no benzoin essential oil. Benzoin Siam mostly comes from Laos, from the Luang Probang area which used to be partly in Thailand. It is also grown in Cambodia and China. Because of its botanical name (Styrax species), benzoin is sometimes confused with styrax.