Chlorine is a yellow-green gas at room temperature. Chlorine has a pungent, irritating odor similar to bleach that is detectable at low concentrations.

Exposure to low concentrations of chlorine (1 to 10 ppm) may cause eye and nasal irritation, sore throat, and coughing. Inhalation of higher concentrations of chlorine gas (>15 ppm) can rapidly lead to respiratory distress with airway constriction and accumulation of fluid in the lungs (pulmonary edema).