A biocide is defined in the European legislation as a chemical substance or micro organism intended to destroy, deter, render harmless, or exert a controlling effect on any harmful organism. US Environmental Protection Agency (EPA) uses a slightly different definition for biocides as "a diverse group of poisonous substances including preservatives, insecticides, disinfectants, and pesticides used for the control of organisms that are harmful to human or animal health or that cause damage to natural or manufactured products". When compared, the two definitions roughly imply the same, although the US EPA definition includes plant protection products and some veterinary medicines.
Term "biocides" and "pesticides" are regularly interchanged, and often confused with "plant protection products". To clarify this, pesticides include both biocides and plant protection products, where the former refers to substances for non-food and feed purposes and the latter refers to substances for food and feed purposes.
When discussing biocides a distinction should be made between a biocidal active substance and a biocidal product. Biocidal active substances are mostly chemical compounds, but can also be micro organisms (e.g. bacteria). Biocidal products contain one or more biocidal active substances and may contain other non-active co-formulants that ensure the effectiveness as well as the desired PH viscosity, Color, odor etc. of a final product. Biocidal products are available on the market for use by professional and/or non-professional consumers.
Although most of biocidal active substances have a relative high toxicity, there are also examples of active substances with low toxicity, such as CO2, which exhibit their biocidal activity only under certain specific conditions such as in closed systems. In such cases, the biocidal product is the combination of active substance and a device that ensures intended biocidal activity, Example of biocidal products available to consumers are products impregnated with biocides (also called treated articles), such as clothes and wristbands impregnated with insecticides, socks impregnated with antibacterial substances etc.
Biocides are commonly used in medicine, agriculture, forestry, and industry. Biocidal substances and products are also employed as anti-fouling agents or disinfectants under other circumstances: chlorine, for example, is used as a short-life biocide in industrial water treatment but as a disinfectant in swimming pools. Many biocides are synthetic, but there are naturally occurring biocides classified as Natural Biocides, derived from, e.g., bacteria and plants.