Limonene and linalool hydroperoxides review: Pros and cons for routine patch testing.

Area of Science:

• Dermatology
• Allergology
• Fragrance Chemistry

Background:

• Limonene and linalool are common fragrance ingredients that can oxidize into hydroperoxides (Lim-OOHs, Lin-OOHs).
• These oxidized compounds are known to cause allergic contact dermatitis, indicated by frequent positive patch test reactions.
• Despite their prevalence and allergenic potential, Lim-OOHs and Lin-OOHs are not routinely included in standard patch testing protocols in Europe.

Purpose of the Study:

• To evaluate the necessity and challenges of patch testing with oxidized limonene and linalool (Lim-OOHs, Lin-OOHs).
• To assess the relevance and interpretation of hydroperoxide patch test results.
• To determine if current patch testing practices for these common fragrance allergens are adequate.

Main Methods:

• Review of existing studies on patch testing with Lim-OOHs and Lin-OOHs.
• Analysis of reported positive reaction rates in patients with dermatitis.
• Examination of challenges in reading and interpreting patch test results, including doubtful or irritant reactions.

Main Results:

• Studies show high percentages of positive patch test reactions to oxidized limonene and linalool in consecutively tested patients.
• A correlation between positive clinical history and strong patch test reactions to these hydroperoxides has been observed.
• Difficulties with interpreting doubtful or irritant reactions have been reported, alongside relevant positive findings.

Conclusions:

• The frequent and relevant positive reactions suggest that patch testing with Lim-OOHs 0.3% and Lin-OOHs 1% may be justified for inclusion in baseline series.
• Further research is needed to determine exposure, sensitization, and elicitation limits for Lim-OOHs and Lin-OOHs in consumer products.
• Improved clinical assessment can be achieved by evaluating prior exposure, potential sensitization, and observed reactions to these oxidized fragrance compounds.