α-Acaridial [2(E)-(4-methyl-3-pentenyl)butenedial] is a novel monoterpene secreted from the house dust mites. Because of its molecular nature of a highly reactive, small lipidic compound, we addressed whether α-acaridial might function as a haptenic allergen that induced allergic contact dermatitis. Mice sensitized with α-acaridial were challenged by the same antigen on the ear skin. After 2 days, significant ear swelling with a prominent infiltration of CD4+ T lymphocytes was observed. In vitro, α-acaridial exhibited an outstanding ability to quickly interact with and chemically modify a reference protein. Virtually all cysteine residues and a sizable fraction of lysine residues were found to be selectively modified, suggesting that α-acaridial could potentially interact with any proteins. Previously, numerous mite-derived proteinaceous allergens have been associated with contact dermatitis. Our study now emphasizes that small lipidic compounds released from mites comprise a new class of mite allergens, and therefore, is of significant medical implications.

Eczema due to contact allergy is usually produced by simple chemicals with the molecules less than 500 KD. A total of 100 cultivated house dust mites (HDM) were extracted with their lipid components in hexane, and they were analyzed by mass measuring gas chromatography. The same components were mixed in petrolatum at 5% or less, and patch tested using Finn Chambers, and the results were read by ICDRG standards. α-Acaridial, contained in Tyrophagus putrescentiae, turned out to have been a primary sensitizer, and could make prurigo reactions. Geranial, a main lipid component in dermatophagoides, showed positive rates at 58.8% at 5% concentration in atopic dermatitis and was expected to cross react to geraniol in cosmetics and soaps. It means that when one is sensitized by HDM, eczema can be provoked and maintained by the usage of ordinary soaps, shampoos and cosmetics, containing geraniol.