Similar term(s): Active substance.
The term “active ingredient” is mostly used in drugs to name the substance
which is pharmaceutically active.
The term “active substance” is also used in biocidal products to name the
component which actually kills, or otherwise controls pests or bacteria.
It is not necessarily the largest or most hazardous component of the product.
Some products may contain more than one active ingredient or substance.
Non-active ingredients are often called inert ingredients.
To read about this term in context:
GreenFacts Summary on Effects of Biocides on antibiotic resistance: