Biocides may be synthetic or naturally occurring chemicals or microorganisms that are intended to destroy, counteract, neutralize, prevent action or otherwise exert control over any organism considered harmful to humans.[1]​.

Biocidal substances generally act at the level of the microorganism's cell membrane, penetrating it and destroying the systems that allow the microorganism to live. The biocide causes the lysis of the protein or lipoprotein wall of the organism and penetrates its interior, interrupting the biochemical reactions that sustain the life of said organism.

They can come in three forms:

• - Physical: High-energy radiation sources (UV light) that oxidize the protein wall and practically burn the microorganism, also superheated water at high pressure.[2]​.

• - Biological: Substances created by higher organisms for self-defense, generally they are of the protein type and are called enzymes. For example: lysozyme.

• - Chemicals: They can be, in turn, inorganic or organically synthesized. For example: chlorine dioxide (ClO), isothiazolines, chloramines, alkyl bromides, alkyl or aryl chlorides, etc.

• - It must have a broad spectrum of activity, that is, it must cover a wide range of microorganisms (bacteria, viruses and fungi).

• - Effective at low concentration: The lower the dose, the more economical the treatment is.

• - Effective over a wide pH range.

• - Soluble in water.

• - Compatible with other chemical species in the medium.

• - High persistence: It must be effective over time.

• - Easy to neutralize "Neutralization (chemical)"): It must have deactivating mechanisms for subsequent neutralization.

• - Low human toxicity: It should not be harmful in safe handling by the operator.

The phenolic coefficient is an experimental value that is carried out on substances that have biocidal properties, taking the biocidal capacity of phenol as a reference.