Mihaly Matura

European Society of Contact Dermatitis guideline for diagnostic patch testing – recommendations on best practice

The present guideline summarizes all aspects of patch testing for the diagnosis of contact allergy in patients suspected of suffering, or having been suffering, from allergic contact dermatitis or other delayed‐type hypersensitivity skin and mucosal conditions. Sections with brief descriptions and discussions of different pertinent topics are followed by a highlighted short practical recommendation. Topics comprise, after an introduction with important definitions, materials, technique, modifications of epicutaneous testing, individual factors influencing the patch test outcome or necessitating special considerations, children, patients with occupational contact dermatitis and drug eruptions as special groups, patch testing of materials brought in by the patient, adverse effects of patch testing, and the final evaluation and patient counselling based on this judgement. Finally, short reference is made to aspects of (continuing) medical education and to electronic collection of data for epidemiological surveillance.

Selected oxidized fragrance terpenes are common contact allergens

Terpenes are widely used fragrance compounds in fine fragrances, but also in domestic and occupational products. Terpenes oxidize easily due to autoxidation on air exposure. Previous studies have shown that limonene, linalool and caryophyllene are not allergenic themselves but readily form allergenic products on air‐exposure. This study aimed to determine the frequency and characteristics of allergic reactions to selected oxidized fragrance terpenes other than limonene. In total 1511 consecutive dermatitis patients in 6 European dermatology centres were patch tested with oxidized fragrance terpenes and some oxidation fractions and compounds. Oxidized linalool and its hydroperoxide fraction were found to be common contact allergens. Of the patients tested, 1.3% showed a positive reaction to oxidized linalool and 1.1% to the hydroperoxide fraction. About 0.5% of the patients reacted to oxidized caryophyllene whereas 1 patient reacted to oxidized myrcene. Of the patients reacting to the oxidized terpenes, 58% had fragrance‐related contact allergy and/or a positive history for adverse reaction to fragrances. Autoxidation of fragrance terpenes contributes greatly to fragrance allergy, which emphasizes the need of testing with compounds that patients are actually exposed to and not only with the ingredients originally applied in commercial formulations.

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.

Patch testing with oxidized R-(+)-limonene and its hydroperoxide fraction.

R‐(+)‐Limonene is an ubiquitous allergen in our environment. It is one of the most widely used fragrance materials not only in fine fragrances but also most often incorporated in domestic and occupational products. Although the non‐oxidized R‐(+)‐limonene itself is not allergenic, it easily forms allergenic products due to autoxidation during handling and storage. 2273 patients at 4 dermatological clinics in Europe were patch tested between 1997 and 1999 in 2 steps. First, the oxidation mixture of R‐(+)‐limonene and 1 selected allergen fraction of the mixture, the limonene hydroperoxides, were tested in 2 different vehicles in consecutive patients. A diverging frequency of positive patch test reactions was observed in the 4 clinics. 3·8% of the consecutive patients tested reacted to oxidized R‐(+)‐limonene in 2 clinics, 6·5% in the 3rd, whereas 0·3% in the 4th clinic. In 2 of the centres, different but significant concomitant positive response rates to other allergens were observed; e.g. to fragrance materials and to colophonium. However, in the total test population, 57% of the limonene‐allergic subjects did not react to any of the fragrance allergy markers used in the standard series. In the 2nd step, patients showing positive reactions were retested, also including additional separate allergens of the limonene oxidation mixture (carvone and limonene oxide). 60% of the limonene‐allergic patients showed positive results at retesting. The limonene hydroperoxide fraction was proved to be the most important allergen of the oxidation mixture, showing positive reactions in around 60% of the limonene‐allergic patients at both test sessions. Testing limonene oxide and carvone separately resulted in very few positive reactions. 3% oxidized R‐(+)‐limonene in non‐stabilized petrolatum is most suitable when using only 1 test preparation for diagnosis of contact allergy to oxidized limonene. Our data give clinical support to the European classification of R‐(+)‐limonene, containing oxidation products, as a skin sensitizer.

Not only oxidized R-(+)- but also S-(-)-limonene is a common cause of contact allergy in dermatitis patients in Europe

Limonene, one of the most often used fragrance terpenes in any kind of scented products, is prone to air‐oxidation. The oxidation products formed have a considerable sensitizing potential. In previous patch test studies on consecutively tested dermatitis patients, oxidized R‐limonene has been proven to be a good and frequent indicator of fragrance‐related contact allergy. The current study extends these investigations to 6 European clinics of dermatology, where the oxidation mixture of both enantiomers of limonene (R and S) have been tested in 2411 dermatitis patients. Altogether, 63 out of 2411 patients tested (2.6%) reacted to 1 or both the oxidized limonene preparations. Only 2.3% reacted to the oxidized R‐limonene and 2.0% to the oxidized S‐limonene. In 57% of the cases, simultaneous reactions were observed to both oxidation mixtures. Concomitant reactions to the fragrance mix, colophonium, Myroxylon pereirae, and fragrance‐related contact allergy were common in patients reacting to 1 or both the oxidized limonene enantiomers. Our study provides clinical evidence for the importance of oxidation products of limonene in contact allergy. It seems advisable to screen consecutive dermatitis patients with oxidized limonene 3% petrolatum, although this patch test material is not yet commercially available.

Linalool - a significant contact sensitizer after air exposure

Background: Linalool is a widely used fragrance terpene. Pure linalool is not allergenic or a very weak allergen, but autoxidizes on air exposure and the oxidation products can cause contact allergy. Oxidized (ox.) linalool has previously been patch tested at a concentration of 2.0% in petrolatum (pet.) in 1511 patients, and 1.3% positive patch test reactions were observed.

Air oxidation increases skin irritation from fragrance terpenes

Background:  Linalool and limonene are common fragrance terpenes that autoxidize on air exposure. The pure compounds are not allergenic but their oxidation products can cause contact allergy. Little has been investigated regarding the irritancy of oxidized terpenes.

Hydroperoxides form specific antigens in contact allergy

Concomitant positive reactions to colophonium, oxidized limonene, and/or oxidized linalool are recorded in patch test studies. The main allergens in these patch test mixtures are hydroperoxides, which form antigens by a radical pathway. Theoretically, concomitant reactions can be explained not only by concomitant sensitization or by true cross‐reactions but also by the hydroperoxides acting as oxidizing agents on skin proteins to form non‐specific antigens without hapten–protein binding. The aim of this study was to explore concomitant reactions and cross‐reactivity patterns among hydroperoxide haptens. We investigated whether individuals allergic to the main allergen in colophonium, 15‐hydroperoxyabietic acid, would also react to limonene hydroperoxide or linalool hydroperoxide. Only 1 of 29 individuals reacted to more than 1 hydroperoxide. The cross‐reactivity pattern among cumene hydroperoxide, limonene hydroperoxide, 1‐(1‐hydroperoxy‐1‐methylethyl) cyclohexene (cyclohexene hydroperoxide), and 15‐hydroperoxydehydroabietic acid was investigated in guinea‐pigs. No general cross‐reactivity was observed. Cross‐reactions between cumene hydroperoxide and cyclohexene hydroperoxide show that similarity in the overall structure and the way of antigen formation are needed. Quantum calculations were used to determine the formation energies of the intermediary radicals. We concluded that hydroperoxides form specific antigens and that formation of non‐specific antigens is unlikely. The concomitant patch test reactions described in the literature are best explained as a result of multiple sensitizations.

Methylisothiazolinone in rinse-off products causes allergic contact dermatitis: a repeated open-application study.

In recent years, the prevalence of contact allergy to the preservative methylisothiazolinone (MI) has increased dramatically. Cosmetic products are one of the major sources of exposure.

High prevalence of contact allergy in adolescence: results from the population-based BAMSE birth cohort

Contact allergy is common among adults. However, little is known about the prevalence in adolescents.