Highly corrosive; can burn the eyes, skin and lungs and is a respiratory irritant. Long-term exposure in the air may lead to ulceration of the nasal passages and chronic skin irritation. If discharged in large quantities, sodium hydroxide can alter the pH of water. In 2005, a large spill of concentrated sodium hydroxide in the Cheakamus River canyon, north of Squamish, B.C., killed virtually all the fish in the river.

Found in: oven cleaners, bathroom cleaners, disinfectants, drain openers, and toilet bowl cleaners.