In brief, this study consisted of two phases. In Phase I, demographic information, the health status of 6500 students, and building and room characteristics of 2117 dorm rooms at Tianjin University were surveyed by questionnaires. The questionnaire survey was anonymous, but building number and room number were reported by participants. Project members visited dorm rooms, distributed questionnaires and explained to participants how to fill out questionnaires. The questionnaires were collected 2 days later. The questions on common cold infections were ''how many times have you had a common cold in the previous 12 months (options: ,6 times; 6-10 times; .10 times)'' and ''how long does a common cold usually last (options: ,2 weeks; 2-4 weeks; .4 weeks)''. Other questions were about frequencies of window opening, cleaning routines and environmental tobacco smoke (ETS) exposure.