When limonene (a citrus fragrance in many beauty products) sits in air, it breaks down into hydroperoxides—versions that are way more allergenic than the original ingredient. Testing patients with these oxidized forms showed high rates of allergic reactions, suggesting limonene hydroperoxides are a major undiagnosed allergen. However, some positive reactions may be irritation rather than true allergies, so results need careful interpretation.

Researchers patch-tested patients suspected of contact dermatitis using limonene hydroperoxides specifically (not regular limonene) to see how often allergic reactions occurred.

Funding not disclosed in abstract