On December 5, 2006, three students at a high school in the Aisne department reported skin irritation. The outbreak escalated rapidly on December 11, 2006, and the school was closed. Epidemiological and environmental investigations were immediately launched to describe the phenomenon and determine its cause. A case was defined as any person attending the high school who exhibited irritation symptoms between December 5, 2006, and January 26, 2007. Data were collected using a standardized questionnaire. A descriptive case study was conducted, followed by a retrospective cohort study of the 1,247 high school students. Indoor air and material analyses were performed. A total of 153 cases were identified. Nearly half of the cases experienced at least one recurrence. The main symptoms reported, pruritus (70%) and erythema (54%), were transient. Two factors were statistically associated with the occurrence of irritation: being female (RR=2.5 p