A newly published scientific study ↗ led by researchers involved in PARC provides important new insights into how exposure to chemical mixtures can influence skin sensitisation ↗ and the elicitation of allergic contact dermatitis ↗, a common inflammatory skin disease affecting millions of people across Europe.

Skin sensitisation and allergic contact dermatitis are traditionally assessed by looking at the effects of single substances in isolation. However, in real-life settings, people are rarely exposed to just one chemical at a time. Instead, exposure often occurs through complex mixtures, particularly in occupational environments, consumer products, and everyday materials. This study addresses a critical gap in current risk assessment approaches by exploring how combinations of chemicals ↗ may interact and modify immune responses in the skin.

The researchers made a systematic review of the existing scientific literature to investigate how chemical mixtures can influence both key phases of allergic contact dermatitis: the sensitisation phase, when the immune system first becomes reactive to a substance, and the elicitation phase, when subsequent exposure triggers a clinical allergic response. The study included 13 papers, and the findings from these indicate that mixtures can alter these processes in ways that are not always predictable based on the effects of individual substances alone.

Jeanne Duus Johansen, project leader, Allergy Research Centre (Gentofte Hospital, Copenhagen, Denmark) highlights:

Our findings, that combinations of irritants and/or skin allergens may lower the threshold of reaction for the individual substance, in a way which is not always predictable, underline the need for risk assessment approaches that better reflect real-life exposure scenarios. A critical gap is the absence of studies on mixtures using New Approach Methodologies (NAMS), which is intended to replace animal testing.

These results reinforce growing scientific evidence that mixture effects are highly relevant for human health risk assessment. In the context of skin allergy, they suggest that current regulatory frameworks based primarily on single-substance assessments may underestimate the real-world risks associated with combined chemical exposures.

The study aligns closely with PARC’s objectives to advance next-generation chemical risk assessment by improving the understanding of mixture toxicity and supporting more realistic and protective approaches to chemical safety. The project continues with more experimental work using NAMs and 3D models of skin. By providing mechanistic insights into how mixtures affect skin sensitisation and elicitation, this work contributes to the scientific basis needed to refine regulatory testing strategies and inform policy development at the European level.

Overall, the findings highlight the importance of integrating mixture considerations into both experimental research and regulatory decision-making, particularly for health outcomes such as allergic contact dermatitis, where cumulative and combined exposures are common.