What does cytotoxicity mean?
Cytotoxicity is the property of being toxic to cells — that is, the capacity of a chemical, drug, or biological agent to damage or kill living cells. The word combines the Greek root for cell with the Latin-derived notion of poison, and it sits at the centre of modern pharmacology, oncology, and toxicology. When scientists develop a new medicine, one of the first safety tests they run measures its cytotoxicity, often by exposing cultured cells to increasing concentrations of the compound and observing how many survive; a cancer therapy ideally shows high cytotoxicity toward tumour cells while sparing healthy ones, which is why the same property can be either a desired effect or a dangerous side effect depending on context. Immunologists also use the term to describe the cell-killing function of specialised immune defenders such as cytotoxic T lymphocytes and natural killer cells. Because it is inherently technical, cytotoxicity appears mainly in laboratory reports, regulatory documents, and scientific writing rather than casual conversation, but it is indispensable vocabulary for anyone reading about drug development, cancer treatment, or immunology.
nounThe quality or degree to which a substance is toxic to cells, causing damage to or death of living cells. It is a key measure in pharmacology, immunology, and toxicology.
- The degree to which a substance or agent damages or kills cells, typically measured in laboratory assays.
- In immunology: the capacity of certain immune cells (such as cytotoxic T lymphocytes and natural killer cells) to destroy target cells.
"Researchers measured the cytotoxicity of the new compound before advancing it to animal trials."
"The cytotoxicity of the chemotherapy drug was tested against healthy liver cells as well as tumour cells."
"Natural killer cells display rapid cytotoxicity against virus-infected targets without prior sensitisation."
Rarely pluralised; the plural may appear when comparing cytotoxicity values across multiple substances or conditions, though writers more often use singular forms or numeric measurements.
"The study compared the cytotoxicities of five candidate compounds across three cell lines."
Your immune system's killer T cells are literally named for it — they're called cytotoxic T cells because their whole job is injecting lethal chemicals into infected cells.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of cytotoxicity
Cytotoxicity derives from two classical roots: 'cyto-', from the Greek 'kytos' meaning hollow vessel or cell, and '-toxic', from the Greek 'toxikon', originally referring to poison used on arrows. The compound adjective 'cytotoxic' was formed in the late nineteenth or early twentieth century as microscopy and cell biology advanced, and the abstract noun 'cytotoxicity' followed as laboratory science required a measurable way to express cell-harming potency. Its cognates include other 'cyto-' terms such as cytoplasm and cytokine, and 'tox-' words such as toxin and toxicology.
Related word forms
How cytotoxicity is actually used
A technical term used almost exclusively in scientific, medical, and regulatory contexts; rarely encountered in everyday speech. In research literature it is usually quantified (e.g., IC50 values) rather than described qualitatively.
Easily confused with cytotoxicity
Toxicity refers to harmfulness to a whole organism in general, whereas cytotoxicity specifically describes harm at the level of individual cells.
Cytology is the study of cells themselves, while cytotoxicity is the property of being poisonous to cells.