Antiseptics, disinfectants and sterilants
Chemicals that kill microbes on skin (antiseptics), on surfaces and instruments (disinfectants), or kill every form including spores (sterilants).
What they are
Antisepsis is applying an agent to living tissue to prevent infection; disinfection destroys most microbes but not spores on inanimate surfaces; sterilisation removes all microorganisms, including spores. Skin antiseptics include chlorhexidine, povidone-iodine and alcohols (ethanol, isopropanol, alcohol-based hand rub). Disinfectants include chlorine compounds, phenolics such as chloroxylenol and quaternary ammonium compounds. Chemical sterilants and high-level disinfectants (glutaraldehyde, ortho-phthalaldehyde, hydrogen peroxide, peracetic acid, ethylene oxide) are used for heat-sensitive instruments such as endoscopes.
Mechanism of action
None of them is selective; they damage structures all microbes share. Alcohols denature proteins and are not sporicidal. Chlorhexidine binds bacterial membranes so that small molecules leak and cytoplasmic proteins precipitate. Iodine, iodophors and chlorine are halogens; chlorine is a strong oxidant whose active form is hypochlorous acid. Phenolics disrupt membranes and precipitate proteins. Aldehydes alkylate proteins and nucleic acids. Peroxygens (hydrogen peroxide, peracetic acid) are powerful oxidants. Ethylene oxide is a gas sterilant for materials that cannot go in the autoclave.
Target: Microbial membranes, proteins and nucleic acids (non-selective)
Drugs in this class
- ChlorhexidineA cationic antiseptic that binds the skin and keeps acting after it dries. In alcohol, it is the preferred skin…Bacterial cell membrane
- Povidone-iodineAn iodophor: iodine carried by a polymer and released slowly to kill bacteria, fungi and many viruses. Used to prepare…Microbial proteins and membranes (free iodine)
Others in the class
- ethanol
- isopropyl alcohol
- alcohol-based hand rub
- chloroxylenol
- sodium hypochlorite (chlorine)
- hydrogen peroxide
- peracetic acid
- glutaraldehyde
- ortho-phthalaldehyde
- ethylene oxide
Test yourself
Think of the answer, then tap the question to see it.
What is the difference between antisepsis, disinfection and sterilisation?
Antisepsis is on living tissue; disinfection kills most microbes but not spores on inanimate objects; sterilisation removes all microorganisms, including spores.
Why must an alcohol-based skin preparation dry before diathermy is used?
Alcohol is flammable; wet solution or pooled vapour can ignite.
Why are quaternary ammonium compounds such as benzalkonium not recommended as antiseptics?
Outbreaks of infection have occurred from Pseudomonas and other gram-negative bacteria growing in quaternary ammonium antiseptic solutions.
Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given.
Sources: Global guidelines for the prevention of surgical site infection (World Health Organization, 2018); WHO guidelines on hand hygiene in health care (World Health Organization, 2009); eEML - Electronic Essential Medicines List (World Health Organization, 2025).
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Representative model, for educational purposes only.