Tea tree oil: contact allergy and chemical composition

In this article, contact allergy to, and the chemical composition of, tea tree oil (TTO) are reviewed. This essential oil is a popular remedy for many skin diseases, and may be used as neat oil or be present in cosmetics, topical pharmaceuticals and household products. Of all essential oils, TTO has caused most (published) allergic reactions since the first cases were reported in 1991. In routine testing, prevalences of positive patch test reactions have ranged from 0.1% to 3.5%. Nearly 100 allergic patients have been described in case reports and case series. The major constituents of commercial TTO are terpinen‐4‐ol, γ‐terpinene, 1,8‐cineole, α‐terpinene, α‐terpineol, p‐cymene, and α‐pinene. Fresh TTO is a weak to moderate sensitizer, but oxidation increases its allergenic potency. The major sensitizers appear to be ascaridole, terpinolene, α‐terpinene, 1,2,4‐trihydroxymenthane, α‐phellandrene, and limonene. The clinical picture of allergic contact dermatitis caused by TTO depends on the products used. Most reactions are caused by the application of pure oil; cosmetics are the culprits in a minority of cases. Patch testing may be performed with 5% oxidized TTO. Co‐reactivity to turpentine oil is frequent, and there is an overrepresentation of reactions to fragrance mix I, Myroxylon pereirae, colophonium, and other essential oils.     

Studies on the autoxidation and sensitizing capacity of the fragrance chemical linalool,identifying a linalool hydroperoxide

Fragrances are among the most common causes of allergic contact dermatitis. The two monoterpenes linalool and d-limonene are the most frequently incorporated fragrance chemicals in scented products. Previous studies on d-limonene show that this monoterpene oxidizes on air exposure (autoxidation) and that allergenic oxidation products are formed. Due to structural similarities, linalool might also form allergenic oxidation products on air exposure. The aim of the present study was to study the autoxidation of linalool and to investigate the sensitizing potential of linalool before and after air exposure. Linalool was oxidized for 10 weeks and gas chromatographic analyses showed that the content of linalool decreased to about 80%. The chromatograms revealed the formation of other compounds during oxidation. One of the major oxidation products was isolated and identified as 7-hydroperoxy-3,7-dimethyl-octa-1,5-diene-3-ol. This substance is, to the best of our knowledge, described for the first time. In sensitization studies in guinea pigs, linalool of high purity gave no reactions, while linalool that had been oxidized for 10 weeks sensitized the animals. It is concluded that autoxidation of linalool is essential for its sensitizing potential.     

Lavender oil lacks natural protection against autoxidation, forming strong contact allergens on air exposure

Background:  Lavender oil is an essential oil frequently used as a fragrance ingredient and in traditional herbal medicine. We have previously studied the effect of air oxidation on the skin sensitizing potency of the monoterpenes linalyl acetate, linalool and β-caryophyllene, the main constituents of lavender oil.
Objective:  The aim of this study was to investigate if the autoxidation observed for the single synthetic terpenes, resulting in strong contact allergens, will take place also in lavender oil.
Methods:  Lavender oil was exposed to air and the autoxidation was followed by chemical analysis. The sensitizing potency before and after air exposure was investigated in mice using the local lymph node assay. Patients with patch test reactions to oxidized linalool were tested to investigate if air-exposed lavender oil could elicit dermatitis in these individuals.
Results:  The terpenes oxidized in air-exposed lavender oil at the same rates as the pure compounds exposed to air, and the same oxidation products were identified. The sensitizing potency of lavender oil increased accordingly on air exposure. Patch testing showed positive reactions to air-exposed lavender oil and also to oxidized linalyl acetate in patients with contact allergy to oxidized linalool.
Conclusion:  This study shows that lavender oil lacks natural protection against autoxidation, and that air-exposed lavender oil can be an important source of exposure to allergenic hydroperoxides.     

The sensitizing capacity of helenin and of two of its main constituents, the sesquiterpene lactones alantolactone and isoalantolactone: a comparison of epicutaneous and intradermal sensitizing methods in different strains of guinea pig

The sensitizing capacities of helenin (an extract from a Compositae Inula helenium L.), alantolactone and isoalantolactone (two isomeric sesquiterpene lactones), were assessed by sensitizing guinea pigs of different strains: albino Himalayan spotted, Pirbright and Hartley. Both alantolactone and isoalantolactone are found to be sensitizers if injected intradermally. Only Pirbright guinea pigs showed a high sensitization rate by the open epicutaneous technique; with this method, alantolactone was the more potent sertsitizer.     

Structure-activity aspects of 4 allergenic sesquiterpene lactones tacking the exocyclic α-methylene at the lactone ring

4 sesquiterpene lactones lacking the exocyclic α-methylene at the lactone ring, but possessing further unsaturated centers such as a cyclopentenone ring or an epoxy group, were proved to be sensitizers in guinea pigs. Lack of substitution in the cyclopentenone ring and unsaturation in the side chains appear to be necessary prerequisites for nucleophilic attack. Our results suggest that to the estimated 650 potential sensitizing sesquiterpene lactones of the Compositae family, a further 50 sesquiterpene lactones should be added.     

Contact allergy to colophony

The sensitizing capacity of 15 commercial colophony products was studied experimentally in guinea pigs. The study included 8 French and 6 American colophony derivatives as well as French tall oil colophony. The results indicate that tall oil colophony is the strongest sensitizing material within the tested group and that the maleic-modified products and the zinc-calcium-resinate are moderate sensitizers. Most of the modified products show a higher sensitizing capacity than the genuine resin acids themselves. Cross-reactions between the resin acids and the derivatives are uncommon. Therefore, patch testing with high concentrations of colophony (e.g., 60%) will not help to detect patients with colophony-derivative allergy.     

Durch Pflanzen ausgelöste toxische und allergische Dermatitis (Phytodermatitis)

Herbal products are being used increasingly for medical or cosmetic purposes. Many cosmetics contain plant extracts for fragrance. Sensitizing plants in cosmetics are tea tree oil, arnica, chamomile, yarrow, citrus extracts, common ivy, aloe, lavender, peppermint, and others. However, the sensitizing potential of these plants varies. Most of the sensitizing substances are sesquiterpene lactones or terpenes. The present paper reviews the various forms of phytodermatitis, including irritant plant dermatitis, phototoxic and photo-allergic dermatitis, allergic dermatitis, and airborne contact dermatitis.     

P37Autoxidation of the fragrance caryophyllene forms contact allergens

This is part of an ongoing effort to investigate how autoxidation affects the sensitzing potential of terpene‐based fragrances. We have previously shown that terpenes such as abeitic acid (diterpene), limonene and linalool (monoterpenes) form stable hydroperoxides when oxidized. These hydroperoxides have proved to be strong allergens. Its therefore of special interest to study the connection between formation of hydroperoxides caused by autoxidation of fragrance chemicals during handling and storage and an increased allergenic effect.
Objective:  To investigate the autoxidation of caryophyllene (sesquiterpene) and study its effect on the sensitizing capacity.
Methods:  Caryophyllene was exposed to air and the autoxidation was monitored by GC and HPLC. The major oxidation products were isolated and their structure determined. The allergenic activity of pure caryophyllene and its oxidation products was investigated in animal assays and clinical testing.
Result:  Only 10% of the staring material remained after 20 weeks of air exposure. The major oxidation product was caryophyllene oxide. Substantial amounts of formaldehyde were found in the oxidation mixture. Little or no hydroperoxides were detected in the total oxidation mixture. Caryophyllene oxide and oxidized caryophyllene showed a low sensitizing capacity in animals and very few positive reactions at patch testing.
Conclusion:  Caryophyllene is easily oxidized at air exposure. A low allergenic effect is observed in both sensitization studies and clinical testing. This is consistent with our earlier findings that the amount of hydroperoxides is important for the allergenic activity of autoxidized terpenes.     

FS06.3Chloroatranol – clinical studies and exposure analysis

Linalool is one of the most frequently used fragrance chemicals in scented products and a large population is exposed to it. It is therefore important to study the allergenic properties of linalool, and the effect of autoxidation.
Objectives:  To study the autoxidation of linalool and identify formed oxidation products, to investigate the impact of autoxidation on the sensitizing capacity and to study the frequency of contact allergy to oxidized linalool among consecutive dermatitis patients.
Methods:  Linalool was air‐exposed and the degradation followed with GC. Oxidation products were identified with GC‐MS and NMR. Pure linalool, 2 different states of oxidized linalool and 3 oxidation products were tested for their sensitizing capacity in the local lymph node assay (LLNA). Consecutive dermatitis patients were patch‐tested with oxidized linalool and a fraction of oxidized linalool.
Results:  Linalool started to decompose immediately when air‐exposed. Several oxidation products were identified among which 3 (2 hydroperoxides and an alpha, beta‐unsaturated aldehyde) contain structural features that make them potential allergens. LLNA showed that the 3 oxidation products were moderate allergens, and that the sensitizing potential of linalool increased with longer air‐exposure times. In the patch‐test study positive reactions were observed to oxidized linalool in 1.65% of the patients.
Conclusions:  The extensively used fragrance chemical linalool is not allergenic in itself. The autoxidation process that takes place at air‐exposure leads to the formation of sensitizing oxidation products. The frequency of consecutive patients reacting to oxidized linalool shows that the experimental findings are clinically important.     

Autoxidation of linalyl acetate, the main component of lavender oil, creates potent contact allergens

Background:  Fragrances are among the most common causes of allergic contact dermatitis. We have in previous studies shown that linalool, present in lavender oil, autoxidizes on air exposure, forming allergenic oxidation products. Oxidized linalool was found to be a frequent cause of contact allergy in a patch test study on consecutive dermatitis patients. Linalyl acetate, the main component of lavender oil is commonly used as a fragrance chemical in scented products. Because of structural similarities, linalyl acetate should also be susceptible to oxidation on air exposure, forming similar oxidation products as linalool.
Objective:  The aim of the present study was to investigate the autoxidation of linalyl acetate and the influence of oxidation on its sensitizing potency.
Methods:  Analyses were performed using gas chromatography, nuclear magnetic resonance spectrometry and mass spectrometry. Sensitizing potencies of compounds were determined using the local lymph node assay (LLNA) in mice.
Results:  Analyses showed that the content of linalyl acetate decreased over time on air exposure and other compounds were formed. Hydroperoxides, an epoxide and an alcohol were identified as oxidation products from linalyl acetate. In the LLNA, linalyl acetate of high purity showed a weak sensitizing potency (EC3 25%). Autoxidation increased the sensitizing potency of linalyl acetate, and a 10 weeks oxidized sample gave an EC3 value of 3.6%. As for linalool, the hydroperoxides were shown to be the oxidation products with the highest sensitizing potency.
Conclusion:  It is concluded that autoxidation of the weakly allergenic linalyl acetate leads to formation of allergenic oxidation products.     

Allergic contact dermatitis to methylenelactones use of lymphocyte transformation test

Summary Seventeen guinea pigs were sensitized to alantolactone, a natural sesquiterpene lactone known for its sensitizing properties, using intradermal injections in Freund's complete adjuvant. Guinea pig skin protein extracts (SPE) were used to make conjugates with alantolactone and an isomer, isoalantolactone. Lymphocyte blastogenesis was observed with SPE-alantolactone conjugates, as well as with guinea pig albumin-lactone conjugates. In six cases, stimulation was noted with unconjugated haptens. These results do not show a high degree of hapten-carrier specificity in contact sensitivity to alantolactone, induced by unconjugated hapten injections. Cross-sensitivity with SPE-isoalantolactone conjugate was also observed.     

Topical use of tea tree oil reduces the dermal absorption of benzoic acid and methiocarb

Tea tree oil (TTO) is a complex mixture of terpene hydrocarbons. Intensive topical use of TTO in different cosmetics and investigations into its potential as an antimicrobial or anti-inflammatory agent has accentuated the need for studies on the toxicity of TTO. We have applied an experimental in vitro model using static diffusion cells with human skin to study penetration characteristics of terpinen-4-ol and the way TTO affects the barrier integrity of the skin and the percutaneous penetration of two chemicals covering a range of solubilities from 0.03 g/l (methiocarb) to 3.0 g/l (benzoic acid). Through GC–MS analysis we identified the major constituents of TTO. In our experimental set-up with full-thickness skin, only the least lipophilic ingredients of TTO penetrated the skin. Barrier integrity was evaluated through measurement of percutaneous penetration of tritiated water. Data indicate that 1% TTO does not affect barrier conditions. The K _p value for tritiated water was increased significantly at 5% TTO, which demonstrate that the barrier integrity is affected at this relatively low concentration of TTO. The barrier integrity is, however, not seriously damaged, but our data indicate an initiated and concentration-dependent effect on the barrier integrity. TTO changed the penetration characteristics for benzoic acid as well as for methiocarb. The general effect was that TTO reduced the maximal flux. For methiocarb, the lag-time was also prolonged by increasing the TTO concentration in the donor phase to 5%. Thus, TTO reduced the overall amount of benzoic acid as well as methiocarb entering the receptor chamber.     

FC04.6Characterisation of dendritic cell responses to ascaridol, an autoxidation product of tea tree oil

A large number of monoterpenes and their degradation products are likely skin sensitizing agents (Hausen et al., 1999). Terpenes are very common e.g., as constituents of cosmetics, food and other daily used products.
We investigated responses to the endoperoxide 1,4‐epidioxy‐2‐p‐menthen (ascaridol), an autoxidation product of tea tree oil, using monocyte derived dendritic cells (MDDC). Therefore, we isolated peripheral blood mononuclear cells (PBMC) from 9 healthy donors by the standard Ficoll‐Paque gradient centrifugation.
Monocytes were isolated by adherence and incubated in media (RPMI 1640) containing GM‐CSF (800 units/ml), IL‐4 (1000 units/ml) and 10% autologous serum. The immature MDDC (day 6) were characterized by flow cytometry (CD1a+, CD14−, CD40, CD45, CD80, CD83, CD86, HLA‐DR and CCR‐7) and incubated with various concentrations of ascaridol (1–70 μg/ml). After one hour incubation time LPS was added (1 μg/ml) for 23 h. Cell culture supernatants were collected after 24 h for cytokine analysis.
IL‐12p40, IL‐12p70 and prostaglandin E2 were measured by ELISA, TNF‐alpha and IL‐2 were measured by flow cytometry (FACS). Methods of the quantification of steady state mRNA levels were established for IL‐12 and CCR7 (real‐time RT‐PCR). Ascaridol enhanced significantly IL‐12p70 production (120% up to 396%) by MDDC as well as mRNA levels for IL‐12 and CCR7. Moreover, we detected a distinct increase of TNF‐alpha (110% up to 146%) secretion, IL‐2 (135%) and PGE2 (102% up to 155%).
Totally, these results suggest that ascaridol may be a potent modulator of maturation and antigen presenting function of dendritic cells, and we performing further experiments to verify this hypothesis.
This study was supported by the Deutsche Forschungsgemeinschaft.     

Contact allergy due to colophony

The sensitizing capacity of 7 commercial modified-colophony products of different origins (esters, polyterpene-modified, phenol-modified, resinate, polymerisate) were studied experimentally in guinea pigs by means of a modified Freund's complete adjuvant (FCA) method. All products showed a weak sensitizing power, but a moderate to strong irritant effect. Within this group, the strongest response was obtained with the calcium resinate. As most of these products are used commercially in paints and lacquers, the risk of acquiring specific hypersensitivity must be considered low.     

Acaricidal activity of Melaleuca alternifolia (tea tree) oil: in vitro sensitivity of sarcoptes scabiei var hominis to terpinen-4-ol

OBJECTIVE: To compare the acaricidal activity of Melaleuca alternifolia (tea tree) oil (TTO) and some of its individual active components on the itch mite Sarcoptes scabiei var hominis. DESIGN: In vitro acaricide sensitivity assessment. SETTING: The Menzies School of Health Research laboratory, located near the Infectious Diseases Ward of the Royal Darwin Hospital, Australia, where patients are admitted and treated for crusted scabies. PARTICIPANTS: Scabies mites (S scabiei var hominis) were collected from a 20-year-old Aboriginal woman admitted to the Royal Darwin Hospital with crusted scabies.Interventions Within 3 hours of collection, scabies mites were placed in continuous direct contact with the TTO products and control acaricides and were observed at regular intervals. MAIN OUTCOME MEASURES: Percentage of mites dead at regular observation intervals between 5 minutes and 24 hours during continuous exposure to the TTO products and acaricides. RESULTS: The 5% TTO and active component terpinen-4-ol were highly effective in reducing mite survival times. Statistically significant differences in mite survival curves were observed for 5% TTO, 2.1% terpinen-4-ol, 5% permethrin, and ivermectin (100 microg/g of Emulsifying Ointment British Pharmacopoeia 88). In vivo effectiveness was also observed. CONCLUSIONS: Documentation of resistance against antiectoparasitic compounds is increasing. Reported S scabiei treatment failures with lindane, crotamiton, and benzyl benzoate, as well as likely emerging resistance to 5% permethrin and oral ivermectin, are of concern and advocate for the identification and development of novel acaricidal drugs. Tea tree oil is a membrane-active biocide extracted from the tree M alternifolia. It is a principal antimicrobial in a wide range of pharmaceuticals sold in Australia, with the main active component being oxygenated terpenoids. The results suggest that TTO has a potential role as a new topical acaricide and confirm terpinen-4-ol as the primary active component.     

Contact allergy due to colophony

Degradation of abietic, levopimaric and dehydroabietic acids after exposure to air and light over a period of one to several months, as well its examination of degraded French tall oil rosin and Portuguese colophony, led to the isolation of numerous oxidation products. These compounds were synthesized and consigned to experimental sensitization in guinea pigs. From 20 substances studied as acids or as their methyl esters, in the present and preceding paper, at least 2 can be named: 8.12-peroxydo-δ¹³⁽¹⁴⁾-dihydroabietic acid and 12 α-hydroxyabietic acid, that contribute a great deal to colophony allergy by both their sensitizing capacity and their determined concentration in the mixture of degradation products. We recommend the preparation of a new mixture oxidation products for patch testing in the diagnosis of contact allergy to colophony.     

The sensitizing capacity of Compositae plants I. Occupational contact dermatitis from Arnica longifolia Eaton

Three patients with occupational contact dermatitis due to Arnica longifolia Eaton and Arnica montana L. are reported. During cultivation, harvesting of the flower heads, chemical investigation of the sesquiterpene lactone constituents and preparation of therapeutic tinctures, they had frequent contact with the plant materials. Patch tests with the two sesquiterpene lactones carabron and helenalin, isolated during investigation from A. lungifolia Eaton, were positive in all three patients, though the second patient had never shown visible allergic reactions of the skin. Sensitization experiments with carabron in five guinea pigs were successful.
The investigation results revealed that carabron, helenalin and the acetyl derivative of helenalin must be considered as the sensitizers of A. longifolia , and helenalin acetate and properly arnifolin as sensitizeis of A. motana.
Studies on cross reactivity in the sensitized animals with six related sesquiterpene lactones showed that only those compounds gave a positive test response which contain an α-methylene γ-lactone group. Cross reactions were obtained with a crude extract of Chrysanthemum indicum L.
The case reports supported by the patch test and investigation results demonstrate that persons handling a new drug from the Compositae family run a risk of developing an allergy after intensive contact with the plant and its constituents.     

Centella asiatica (Indian pennywort), an effective therapeutic but a weak sensitizer

The sensitizing capacity of Centella asiatica (raw extract) and its triterpenic constituents asiaticoside, asiatic acid and madecassic acid has been studied in guinea pigs. The extract itself as well as the 3 acids were found to be very weak sensitizers. Centella asiatica extract is used effectively in the treatment of keloids, leg ulcers, phlebitis, slow-healing wounds, leprosy, surgical lesions, striae distensae and cellulitis. Athough applied frequently to damaged skin, the risk of acquiring contact sensitivity to this plant or its constituents is low.     

Contact allergy due to colophony (VII), Sensitizing studies with oxidation products of abietic and related acids

9 oxidation products of abietic acid, dehydroabietic acid, and levopimaric acid were prepared synthetically to determine their sensitizing potential in guinea pigs. It was found that compounds with epoxy and peroxo groups in rings A and B had a notable sensitizing potential. The same result was found with 7-oxode-hydroabietic acid identified earlier in rosin (3) and a polar fraction obtained from commercial abietic acid, suggesting the presence of still unidentified oxidation products. Hydroxylation of rings A or B, or conversion to the methyl esters, considerably decreases the sensitizing potential. A model is presented underlining the importance of hydrophobic and polar domains addition to chemically reactive groupings, in the allergen. Insertion into the lipid bilayer may play an important rôle in contact sensitivity.     

The sensitizing capacity of Compositae plants. VI. Guinea pig sensitization experiments with ornamental plants and weeds using different methods

Experimental studies in guinea pigs using ether extracts of 20 different species of the Compositae plant family were carried out with the open epicutaneous method (OET) and the guinea pig maximization test (GPMT). The results demonstrate that Cnicus benedictus (blessed thistle), Chrysanthemum leucanthemum (marguerite, ox-eye daisy) and Helianthus debilis (dwarf sunflower) are strong sensitizers while Helenium amarum (bitterweed), Gaillardia amblyodon (blanket flower), Artemisia ludoviciana (prairie sage), Ambrosia trifida (giant ragweed) and Solidago virgaurea (goldenrod) are medium sensitizers. Twelfe species revealed only a weak or no sensitizing capacity; among those were corn flower, wormwood, mugwort, coltsfoot and dandelion. Cross-reactivities were observed in a considerable number of the investigated plant species. The sensitizing power as well as the observed cross-reactions depend on the occurrence of sesquiterpene lactones which have an alpha-methylene group exocyclic to the lactone in common ("immunologic requisite"). As a practical consequence, patients suffering from allergic contact dermatitis due to Compositae species are strictly requested to avoid contact with the offending species and all related species to prevent recurrences of their skin lesions.