What is a chemical called that can cause a severe allergic reaction?

A chemical that can cause a severe allergic reaction is referred to as a sensitizer. Sensitizers provoke an immune response after repeated exposure, leading to allergic reactions in susceptible individuals. The body's immune system becomes primed to respond to the sensitizer, and subsequent exposures can trigger more severe reactions, such as anaphylaxis in some cases.

In contrast, allergens are substances that can cause allergic reactions, but not all allergens are sensitizers. A toxin refers to a poisonous substance produced by living organisms that can cause harm but does not specifically relate to allergic reactions. A pathogen is an infectious agent that can cause disease but is not inherently linked to allergies. Understanding these distinctions helps identify the appropriate terms and their respective roles in emergency response scenarios involving hazardous materials and biological threats.