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.