Kaolin has a TLV (threshold limit value) of 2.0 milligrams per cubic meter of air breathed. By comparison iron oxide is considered a safe-to-use material at 5.0, tin oxide is 2.0, barium carbonate is 0.5, quartz is 0.1-0.05.
Some books cite the presence of some free silica in kaolin as a silicosis hazard; however, other sources and regulatory bodies recognize no known hazards and consider it a nuisance dust. Unlike ball clay, kaolin normally only contains small amounts of quartz (e.g. 1%).
Like many clays, data sheets often caution against slipping on a slippery aqueous suspension if it gets spilled on the floor.
ALLERGIES: It unusual to be allergic to an inert mineral like clay. However, molds, mildews, and other organisms that can make their home in clay, along with their byproducts, can cause a problem.