A biohazard is a biological substance that's dangerous to people or the environment. Many biohazards are made of bacteria or other microorganisms.

Some biohazards are an unintentional side effect of biologists working with or studying toxins or viruses. One common type of biohazard is medical waste — things like used syringes or other tools contaminated with human blood, bacteria, or other microorganisms. The word biohazard was first used around 1973, from the Greek bio-, "life," and hazard, from the Old French hasard, "game of chance."

Definitions of biohazard

n hazard to humans or the environment resulting from biological agents or conditions

Type of:
health hazard
hazard to the health of those exposed to it

n any bacterium or virus or toxin that could be used in biological warfare

biological agent
Type of:
an active and efficient cause; capable of producing a certain effect

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