Burglars spread an unknown substance in the area after a break-in at Parker Building Supplies in Uckfield overnight.
Police are investigating the burglary at Bellbrook Industrial Estate in Uckfield.
They said it happened at about 1.30am and a quantity of insulation sheeting – valued at between £6,000 and £8,000 – was stolen.
“The suspects fled the scene and covered the area with an unknown substance which caused a small number of people issues such as sore throats. They were checked over and did not require hospital treatment.”
Police added the substance was confirmed to be non-corrosive, and both East Sussex Fire and Rescue Service and South East Coast Ambulance Service stood down from the scene before midday.
Police enquiries are ongoing, and anyone who witnessed the burglary, or who has any information about the incident, is asked to report it online or call 101, quoting serial 246 of 30/07.