The toxicity of arsenic depends on its chemical state. Metallic arsenic and arsenious sulfides are inert or nearly so, while arsine, AsH3, a gas, is extremely toxic. Arsenical compounds are in general hazardous, principally because of their irritant effects on the skin. Men handling arsenic trioxide industrially wear special clothing and masks which frequently are changed; otherwise, dermatitis may result particularly in the folds of the skin or moist areas.

Poisoning by means of inhalation of dusts or fumes are unusual but care should be taken and ventilation should be installed. Most poisoning is due to ingestion.