Assessment of the sensitizing potency of preservatives with chance of skin contact by the loose-fit coculture-based sensitization assay (LCSA)

Health safety of parabens evaluated by selected in vitro methods

Seven selected parabens (4 allowed, 3 banned in cosmetics) were tested in order to confirm and expand historical data on their toxicological properties and safety. The aim was to apply novel in vitro methods, which have been sufficiently technically and scientifically validated for the purposes of toxicological testing of chemicals. The study included several toxicological endpoints such as skin/eye irritation, skin sensitization, endocrine disruption and genotoxicity. The battery of selected methods comprised regulatory accepted EpiDerm™ skin model (OECD TG 439); EpiOcular™ corneal model (OECD TG 492) and scientifically valid test method HET-CAM (DB-ALM Protocol No. 47); in chemico test DPRA (OECD TG 442C); in vitro test LuSens (OECD TG 442D) and in vitro test h-CLAT (OECD TG 442E); Ames MPF™ (Xenometrix) and XenoScreen YES/YAS (Xenometrix). Overall, none of the 4 allowed parabens exhibited skin/eye irritation or genotoxicity. However, all allowed parabens in cosmetics were predicted as samples with potentially sensitizing properties in the LuSens and h-CLAT test methods, but not confirmed by DPRA. Endocrine disruption was recorded only at high concentrations, whereas methyl paraben and ethyl paraben exhibited the lowest activity. This study confirmed the safety of use of the allowed parabens in the highest recommended concentrations in cosmetics or pharmaceuticals.

Amended Safety Assessment of Parabens as Used in Cosmetics

The Expert Panel for Cosmetic Ingredient Safety (Panel) assessed the safety of 21 parabens as preservatives in cosmetic products. All of these ingredients are reported to function in cosmetics as preservatives; however, 5 are reported to also function as fragrance ingredients. The Panel reviewed relevant data relating to the safety of these ingredients under the reported conditions of use in cosmetic formulations. The Panel concluded that 20 of the 21 parabens included in this report are safe in cosmetics in the present practices of use and concentration described in this safety assessment when the sum of the total parabens in any given formulation does not exceed 0.8%. However, the available data are insufficient to support a conclusion of safety for benzylparaben in cosmetics.

Sensitive Skin Syndrome: An Update

Sensitive skin syndrome is a widely reported complaint but a diagnostic challenge because of its subjective symptoms and lack of clearly visible manifestations. Epidemiological studies have shown the prevalence of sensitive skin to be as high as 60-70% among women and 50-60% among men. Patients with this syndrome usually have unpleasant sensations when exposed to physical, thermal, or chemical stimuli that normally cause no provocation on healthy skin. Recent studies and newly accepted position papers have provided a more in-depth understanding and consensus of its underlying pathophysiology, associations, diagnosis, and treatment. Since no clinical studies have been conducted about specific treatment protocols, patients with this condition should be provided with personalized skin management. Given this updated knowledge, our review offers an approach to sensitive skin syndrome, with differential diagnoses, and interventions targeting its pathophysiology.

Skin Sensitization to Fluorescein Isothiocyanate Is Enhanced by Butyl Paraben in a Mouse Model

Contact hypersensitivity (CHS) to preservatives is receiving increased attention. Parabens are widely used in foods, pharmaceutics and cosmetics as preservatives. The skin sensitizing activity of parabens remains controversial but a few investigations have been made as to whether parabens could facilitate sensitization to other chemicals. We have shown that di-n-butyl phthalate (DBP), a phthalate ester, has an adjuvant effect in a fluorescein isothiocyanate (FITC)-induced CHS mouse model. We have also demonstrated that DBP activates transient receptor potential ankyrin 1 (TRPA1) cation channels expressed on sensory neurons. Comparative studies of phthalate esters revealed that TRPA1 agonistic activity and the adjuvant effect on FITC-CHS coincide. Here we focused on two commonly used parabens, butyl paraben (BP) and ethyl paraben (EP), as to their adjuvant effects. BALB/c mice were epicutneously sensitized with FITC in acetone in the presence or absence of a paraben. Sensitization to FITC was evaluated as the ear-swelling response after FITC challenge. BP but not EP enhanced skin sensitization to FITC, but the effect of BP was much weaker than that of DBP. Mechanistically, BP enhanced the trafficking of FITC-presenting CD11c⁺ dendritic cells (DCs) from the skin to draining lymph nodes as well as cytokine production by draining lymph nodes. When the TRPA1 agonistic activity was measured with a cell line expressing TRPA1, BP exhibited higher activity than EP. The present study provides direct in vivo evidence that BP causes sensitization to other chemicals by means of a mouse FITC-CHS model.

State of the art in non-animal approaches for skin sensitization testing: from individual test methods towards testing strategies

The hazard assessment of skin sensitizers relies mainly on animal testing, but much progress is made in the development, validation and regulatory acceptance and implementation of non-animal predictive approaches. In this review, we provide an update on the available computational tools and animal-free test methods for the prediction of skin sensitization hazard. These individual test methods address mostly one mechanistic step of the process of skin sensitization induction. The adverse outcome pathway (AOP) for skin sensitization describes the key events (KEs) that lead to skin sensitization. In our review, we have clustered the available test methods according to the KE they inform: the molecular initiating event (MIE/KE1)-protein binding, KE2-keratinocyte activation, KE3-dendritic cell activation and KE4-T cell activation and proliferation. In recent years, most progress has been made in the development and validation of in vitro assays that address KE2 and KE3. No standardized in vitro assays for T cell activation are available; thus, KE4 cannot be measured in vitro. Three non-animal test methods, addressing either the MIE, KE2 or KE3, are accepted as OECD test guidelines, and this has accelerated the development of integrated or defined approaches for testing and assessment (e.g. testing strategies). The majority of these approaches are mechanism-based, since they combine results from multiple test methods and/or computational tools that address different KEs of the AOP to estimate skin sensitization potential and sometimes potency. Other approaches are based on statistical tools. Until now, eleven different testing strategies have been published, the majority using the same individual information sources. Our review shows that some of the defined approaches to testing and assessment are able to accurately predict skin sensitization hazard, sometimes even more accurate than the currently used animal test. A few defined approaches are developed to provide an estimate of the potency sub-category of a skin sensitizer as well, but these approaches need further independent evaluation with a new dataset of chemicals. To conclude, this update shows that the field of non-animal approaches for skin sensitization has evolved greatly in recent years and that it is possible to predict skin sensitization hazard without animal testing.