A residence hall at California State University, Fresno, was evacuated Sunday night after an unknown substance fouled the air in a third-floor hallway, officials said.
Students and staff at Graves Hall left the building at 11:15 p.m. and remained outside for about two hours, Fresno State spokeswoman Shirley Armbruster said.
No one was seriously injured.
Between 25 and 30 students reported scratchy throats, itchy eyes and coughing.
The Fresno Fire Department's hazardous materials team and American Ambulance were called to the hall.
Students were examined by paramedics and determined to be unhurt, Armbruster said.
About 200 students and five staff members were in the hall when the incident occurred.
The incident is being investigated by university police and housing officials.