Repeated Exposure to Hydroperoxides of Linalool Induces Immunologically Verified Allergic Contact Dermatitis.

Summary

In sensitized individuals, linalool hydroperoxides elicited allergic contact dermatitis in a dose-dependent manner during both patch testing and a 21-day ROAT, with 1.0% emerging as the most reliable patch test concentration. Molecular profiling showed upregulation of IL1 family genes, Th2-associated markers (IL4, GATA3), and CCL22, validating an immune mechanism.

Key Findings

• 1.0% Lin-OOH was the most reliable concentration for confirming allergy on patch testing.
• ROAT elicited positive reactions in sensitized subjects at 0.163% (33%), 0.054% (17%), and 0.018% (8%); no positives occurred in controls.
• Biopsy RT-qPCR showed upregulation of IL1β, IL1RN, IL4, GATA3, and CCL22, consistent with an allergic immune response.
• Dose-dependent elicitation was observed across both patch testing and simulated-use ROAT.

Clinical Implications

Use 1.0% linalool hydroperoxides for confirmatory patch testing; counsel sensitized patients on avoidance. Data support setting maximum use levels/stability requirements to limit Lin-OOH formation in cosmetic products.

Limitations

• Small sample size may limit generalizability
• Short-term simulated perfume exposure may not capture all real-world usage patterns

Future Directions

Larger, multi-center dose–response studies including diverse product matrices; evaluate stabilization strategies and regulatory limits to reduce in-use Lin-OOH formation.