The optimal patch test concentration for ascaridole as a sensitizing component of tea tree oil

Electron paramagnetic resonance and spin trapping to detect free radicals from allergenic hydroperoxides in contact with the skin: from the molecule to the tissue

A major research topic consists of revealing the contribution of radical-mediated reactions in dermatological diseases related to xenobiotic-induced stress, to succeed risk assessment procedures protecting producers and consumers. Allergic contact dermatitis is the clinically relevant consequence of skin sensitization, one of the most critical occupational and environmental health issues related to xenobiotics exposure. The first key event identified for the skin sensitization process to a chemical is its aptitude to react with epidermal proteins and form antigenic structures that will further trigger the immune response. Many chemical sensitizers are suspected to react through mechanisms involving radical intermediates. This review focuses on recent progress we have accomplished over the last few years studying radical intermediates derived from skin sensitizing chemicals by electron paramagnetic resonance in combination with the spin trapping technique. Our work is carried out "from the molecule", performing studies in solution, "to the tissue", by the development of a methodology on a reconstructed human epidermis model, very close in terms of histology and metabolic/enzymatic activity to real human epidermis, that can be used as suitable biological tissue model. The benefits are to test chemicals under conditions close to human use and real-life sensitization exposures and benefit from the 3D microenvironment. This article is protected by copyright. All rights reserved.

Risks associated with cosmetic ingredients

The media and social networks often echo fears about the potential toxicity of cosmetics and the dangers they pose to the environment. Dermatologists may be asked about these topics, but despite regulatory labelling constraints and the proliferation of specialized sites and applications, they do not always have access to reliable information. It is for this reason that we are providing the present overview of current knowledge on the subject.

Recent advances in understanding and managing contact dermatitis

About 20% of the general population is contact-sensitized to common haptens such as fragrances, preservatives, and metals. Many also develop allergic contact dermatitis (ACD), the clinical manifestation of contact sensitization. ACD represents a common health issue and is also one of the most important occupational diseases. Although this inflammatory skin disease is mediated predominantly by memory T lymphocytes recognizing low-molecular-weight chemicals after skin contact, the innate immune system also plays an important role. Along that line, the presence of irritants may increase the risk of ACD and therefore ACD is often seen in the context of irritant contact dermatitis. In this review article, we discuss recent progress in basic research that has dramatically increased our understanding of the pathomechanisms of ACD and provides a basis for the development of novel diagnostic and therapeutic measures. Current methods for diagnosis as well as treatment options of ACD are also discussed.

What Happens after Activation of Ascaridole? Reactive Compounds and Their Implications for Skin Sensitization

To replace animal testing and improve the prediction of skin sensitization, significant attention has been directed to the use of alternative methods. The direct peptide reactivity assay (DPRA), the regulatory agencies' approved alternative in chemico method, has been applied for understanding the sensitization capacity of activated ascaridole. Ascaridole, the oxidative metabolite of α-terpinene, is considered to be one of the components responsible for the contact allergy associated with essential oils derived from Chenopodium and Melaleuca species. The recently developed high-throughput screening based on the dansyl cysteamine (HTS-DCYA) method was applied to understand the reported enhanced reactivity of activated ascaridole and possibly to identify the resulting elusive radical or other reactive species. For the first time, a substituted cyclohexenone was identified as a potential electrophilic intermediate resulting in higher depletion of nucleophilic DCYA, along with several nonreactive byproducts of ascaridole via a radical degradation mechanism. Formation of electrophilic species via radical degradation is one of the possible pathways should be considered for the peptide reactivity of in aged tea tree oil or oils rich in terpinenes along with commonly believed reactants, allylic-epoxides and allylic-peroxides.

Contact allergy to essential oils cannot always be predicted from allergy to fragrance markers in the baseline series

BACKGROUND

Essential oils are fragrance substances that are labelled on cosmetic products by their INCI names, potentially confusing consumers.

OBJECTIVES

To establish whether contact allergy to essential oils might be missed if not specifically tested for.

METHODS

We tested 471 patients with 14 essential oils and 2104 patients with Melaleuca alternifolia oil between January 2008 and June 2014. All patients were tested with fragrance mix I, fragrance mix II, hydroxyisohexyl 3-cyclohexene carboxaldehyde, and Myroxylon pereirae. Three hundred and twenty-six patients were tested with hydroperoxides of limonene and linalool.

RESULTS

Thirty-four patients had a +/++/+++ reaction to at least one essential oil. Eleven had no reaction to any of the six marker fragrance substances. Thus, 4 of 11 positive reactions to M. alternifolia oil, 2 of 7 reactions to Cymbopogon flexuosus oil, 1 of 5 reactions to Cananga odorata oil, 3 of 4 reactions to Santalum album oil and 2 of 3 reactions to Mentha piperita oil would have been missed without individual testing.

CONCLUSION

A small number of patients who are allergic to essential oils could be missed if these are not specifically tested. Labelling by INCI names means that exposure may not be obvious. Careful inspection of so-called 'natural' products and targeted testing is recommended.