Animal experiments on the allergenicity of d-limonene--the citrus solvent

Contact sensitization to hydroperoxides of limonene and linalool: Results of consecutive patch testing and clinical relevance

Background

Hydroperoxides of limonene and linalool are potent sensitizers.

Objectives

To investigate the prevalence of contact allergy to both hydroperoxides of limonene and hydroperoxides of linalool, to report clinical relevance, and to investigate patient demographics.

Methods

A total of 821 patients (35.6% male, mean age 42.4 years ± 17.8 years) were consecutively patch tested with our departmental baseline series and our fragrance series, including hydroperoxides of limonene 0.3% pet. and hydroperoxides of linalool 1.0% pet. The clinical relevance was assessed for all positive reactions.

Results

Positive patch test reactions to hydroperoxides of limonene and to hydroperoxides of linalool were observed in 77 patients (9.4%, 95% confidence interval [CI]: 7.4%‐11.4%) and in 96 patients (11.7%, 95%CI: 9.5%‐13.9%), respectively; 38 of these patients (4.6%, 95%CI: 3.2%‐6.0%) reacted to both. Most reactions were considered to be possibly or probably clinically relevant (66.3% and 68.8%, respectively), and a small proportion were deemed to be of certain clinical relevance (18.2% and 19.8%, respectively).

Conclusion

As compared with previous studies, high numbers of positive reactions to both hydroperoxides of limonene and hydroperoxides of linalool were observed, the majority of which were clinically relevant, supporting their inclusion in the European baseline series.

Oxidized limonene and oxidized linalool - concomitant contact allergy to common fragrance terpenes

BACKGROUND

Limonene and linalool are common fragrance terpenes. Both oxidized R-limonene and oxidized linalool have recently been patch tested in an international setting, showing contact allergy in 5.2% and 6.9% of dermatitis patients, respectively.

OBJECTIVE

To investigate concomitant reactions between oxidized R-limonene and oxidized linalool in consecutive dermatitis patients.

METHODS

Oxidized R-limonene 3.0% (containing limonene hydroperoxides 0.33%) and oxidized linalool 6% (linalool hydroperoxides 1%) in petrolatum were tested in 2900 consecutive dermatitis patients in Australia, Denmark, Singapore, Spain, Sweden, and the United Kingdom.

RESULTS

A total of 281 patients reacted to either oxidized R-limonene or oxidized linalool. Of these, 25% had concomitant reactions to both compounds, whereas 29% reacted only to oxidized R-limonene and 46% only to oxidized linalool. Of the 152 patients reacting to oxidized R-limonene, 46% reacted to oxidized linalool, whereas 35% of the 200 patients reacting to oxidized linalool also reacted to oxidized R-limonene.

CONCLUSIONS

The majority of the patients (75%) reacted to only one of the oxidation mixtures, thus supporting the specificity of the reactions. The concomitant reactions to the two fragrance allergens suggest multiple sensitizations, which most likely reflect the exposure to the different fragrance materials in various types of consumer products. This is in accordance with what is generally seen for patch test reactions to fragrance materials.

Safety evaluation and risk assessment of d-Limonene

d-Limonene, a major constituent of citrus oils, is a monoterpene widely used as a flavor/fragrance additive in cosmetics, foods, and industrial solvents as it possesses a pleasant lemon-like odor. d-Limonene has been designated as a chemical with low toxicity based upon lethal dose (LD50) and repeated-dose toxicity studies when administered orally to animals. However, skin irritation or sensitizing potential was reported following widespread use of this agent in various consumer products. In experimental animals and humans, oxidation products or metabolites of d-limonene were shown to act as skin irritants. Carcinogenic effects have also been observed in male rats, but the mode of action (MOA) is considered irrelevant for humans as the protein α(2u)-globulin responsible for this effect in rodents is absent in humans. Thus, the liver was identified as a critical target organ following oral administration of d-limonene. Other than the adverse dermal effects noted in humans, other notable toxic effects of d-limonene have not been reported. The reference dose (RfD), the no-observed-adverse-effect level (NOAEL), and the systemic exposure dose (SED) were determined and found to be 2.5 mg/kg/d, 250 mg/kg//d, and 1.48 mg/kg/d, respectively. Consequently, the margin of exposure (MOE = NOAEL/SED) of 169 was derived based upon the data, and the hazard index (HI = SED/RfD) for d-limonene is 0.592. Taking into consideration conservative estimation, d-limonene appears to exert no serious risk for human exposure. Based on adverse effects and risk assessments, d-limonene may be regarded as a safe ingredient. However, the potential occurrence of skin irritation necessitates regulation of this chemical as an ingredient in cosmetics. In conclusion, the use of d-limonene in cosmetics is safe under the current regulatory guidelines for cosmetics.

A novel xylene substitute for histotechnology and histochemistry

Propylene glycol methyl ether (PGME) exhibits excellent solvent and coupling properties. A toxicity database provided evidence suggesting that PGME might be a useful substitute for xylene in histotechnology and histochemistry applications. Tissue specimens were fixed, cleared in either PGME or xylene, embedded in paraffin wax, then dewaxed in either PGME or xylene. Sections were treated with the following stains: hematoxylin & eosin (H & E), three special stains of the Gordon/Sweet silver staining method, PAS, and Masson's trichrome, and immunostains including actin, CD3, CD34, CK, CK7/CK9, Ki-67, and ER/PR. The sections were mounted in a resinous medium consisting of PGME and pinene copolymer, then examined under a microscope. Variables such as water tolerance, dimension change, organic solvency, and anti-fading efficacy also were assessed. Depending on the application, PGME performance was equal to or exceeded that of xylene. PGME provided better optical clarity and nuclear detail, did not harden the tissue samples, conserved tissue antigenicity, and was amenable to resinous mounting. Tissues not dehydrated with absolute ethanol also were processed properly. Tissues treated with PGME did not warp or contract compared to those treated with xylene (p < 0.0001). PGME, however, exhibited less organic solvency than xylene. There was no discernible change in the colors of stains in sections processed with PGME even after storage for two years. These results suggest that PGME is a novel xylene substitute for applications in histotechnology and histochemistry.

Occupational contact dermatitis to a limonene-based solvent in a histopathology technician

Recently, D-limonene-based solvents are used as a safe alternative to xylene for histological and cytological application to dissolve paraffin. We report the case of a histopathology technician with a recalcitrant hand contact dermatitis strictly related to the use of a limonene-based solvent agent. Patch tests with SIDAPA (Italian Society of Allergological, Professional and Environmental Dermatology) standard series, limonene-based solvent used by the patient and D- and L-limonene (both oxidized and nonoxidized form) and with Giemsa and methylene blue stains were performed. Patch testing gave positive results to oxidized D- and L-limonene. The patient retired from work and promptly improved and healed the hand eczema. Subsequently, the potential occurrence of limonene oxidation products in the incriminated preparation was investigated using gas chromatography-mass spectrometry. While patch test showed positive reaction to oxidized limonene, chemical analysis failed to detect oxidized limonene in the preparations used by the patient. Considering the strict relation between the use of the preparations and the appearance of symptoms, we can assume that oxidized limonene may be produced during the handling of limonene-based products, especially in the presence of oxidants stains, frequently used in histological laboratories.

Toxicity Study of the Volatile Constituents of Myoga Utilizing Acute Dermal Irritation Assays and the Guinea‐Pig Maximization Test

Myoga is a fragrant plant which is the special product of Japan and is cultivated throughout Japan. According to our earlier investigation (unpublished data) of myoga cultivators in Japan, 8 of 35 cultivators experienced contact dermatitis in the harvest season. The purpose of this study was to assess the allergenicity of myoga and its major volatile components. The volatile components of myoga were analyzed by gas chromatograph (GC). They included a-pinene, beta-pinene and R-(+)-limonene. We performed a toxicity study of each of the major fragrant components of myoga using acute dermal irritation assays and the Guinea-Pig Maximization test (GPMT) in order to probe the mechanism of allergic contact dermatitis. In acute dermal irritation assays, alpha-pinene, beta-pinene and limonene showed positive responses at concentrations of 4%; limonene oxide at 20% and myoga showed a positive response at concentrations of 100%. From the results of the GPMT, according to Kligman scores, limonene oxide was identified as an extreme skin sensitizer and myoga as a mild skin sensitizer. The results of the present study show that R-(+)-limonene is the most important allergen amongst the chemical components of myoga, and we consider it to be the reason why myoga cultivators experience allergic contact dermatitis.

Oxidized citrus oil (R-limonene): a frequent skin sensitizer in Europe

BACKGROUND

Peel oil from citrus fruits consists of R-(+)-limonene, which is one of the most commonly used fragrance materials in technical products and in fine fragrances. This substance forms allergenic oxidation products during handling and storage.

OBJECTIVE

We wanted to study the frequency of allergic reactions to oxidized R-(+)-limonene in patients with dermatitis and find a suitable test preparation.

METHOD

Patch testing with oxidized R-(+)-limonene was performed on 2273 patients at 4 dermatology clinics in Europe.

RESULTS

Of the consecutive patients tested, 3.8% to 3.9% had positive reactions in two of the clinics; 6.5% had positive reactions in the third clinic; and 0.3% had positive reactions in the fourth clinic. A total of 63 patients showed positive reactions. In total, 57% of the patients did not react to fragrance mix or balsam of Peru. We recommend testing with 3% oxidized R-(+)-limonene in patients referred for patch testing.

CONCLUSION

The high frequency of oxidized limonene allergy provides clinical evidence for the European classification of R-(+)-limonene that contains oxidation products as skin sensitizers.

Melaleuca oil (tea tree oil) dermatitis

BACKGROUND

Melaleuca oil (tea tree oil) is the essential oil distilled from the leaves of Melaleuca alternifolia Cheel. Tea tree oil is popular for treating various cutaneous maladies.

OBJECTIVE

Our purpose was to determine which constituent compounds of Melaleuca oil are responsible for allergic contact eczema in seven patients who became sensitized.

METHODS

The seven patients were patch tested with Finn Chambers to a 1% solution (vol/vol) of melaleuca oil and 1% solutions (vol/vol) of 11 constituent compounds.

RESULTS

Of seven patients reactive to the 1% melaleuca oil solution, six patients also reacted to limonene, five to alpha-terpinene and aromadendrene, 2 to terpinen-4-ol, and one each to p-cymene and alpha-phellandrene. d-Carvone, an autooxidative derivative of limonene, caused no reactions among the seven patients.

CONCLUSION

d-Limonene was the most common allergen causing allergic contact eczema in our patients. Clinicians are likely to see more contact eczema caused by the increasing use of this popular nostrum.

d-limonene exposure to humans by inhalation: uptake, distribution, elimination, and effects on the pulmonary function

The toxicokinetics of d-limonene were studied in human volunteers exposed by inhalation (2 h, work load 50 W) in an exposure chamber on three different occasions. The exposure concentrations were approximately 10, 225, and 450 mg/m3 d-limonene. The relative pulmonary uptake was high, approximately 70% of the amount supplied. The blood clearance of d-limonene observed in this study, 1.1 l kg-1 h-1, indicates that d-limonene is metabolized readily. About 1% of the total uptake was eliminated unchanged in the expired air after the end of exposure, while approximately 0.003% was eliminated in the urine. A long half-time in blood was observed in the slow elimination phase, which indicates accumulation in adipose tissues. A decrease in vital capacity was observed after exposure to d-limonene at a high exposure level. The subjects did not experience any irritative symptoms or symptoms related to the central nervous system (CNS).