Abstract Occupational cases with allergic reaction to fragrance substances, which refer to various chemicals providing aroma characteristics, are arising with its recent usage diversification from pharmaceutical, perfume industry to aromatic remedies. However, chemicals responsible for fragrance allergy have hardly been identified because its component is complex and its sensitization is not frequent. This report will present a case of acute allergic dermatitis that is likely induced by 3-hexylthiophene, one of aromatic compounds often contained in fragrance substances. The case, who was a 27-year male researcher engaged in organic chemical synthesis for six years, was exposed to 3-hexylthiophene and its product (2-bromo-3-hexylthiophene) through an experiment in May 2004 and itching, swelling and eczema immediately developed from face to back. This case of sensitization to 3-hexylthiophene suggests that it be a possible allergen for fragrance allergy.