Cytotoxicity is the term used to describe the effect of a substance where it is harmful to living cells.
Both toxins and pharmaceuticals may have cytotoxic effects and, for a pharmaceutical, the cytotoxic effect may in fact be the therapeutic effect rather than a side effect. For example, antibiotics are clearly cytotoxic to many types of bacteria, although not to human cells, viruses or fungi. In addition, most chemotherapy agents are cytotoxic, which is the therapeutic and side effect of the drug. Cells of the immune system are also cytotoxic.
A cytotoxin may work in one of several ways:
- It can destroy the cell wall of the cell
- It can prevent the cell from duplicating
- It can activate the cell's own mechanism to destroy itself that occurs when the organism dies
However, not all toxins are cytotoxic. Many, like cyanide and botulism, merely affect the transmission of physiological processes such as nerve transmission. Some natural venoms, like those of snakes and spiders, can be extremely cytotoxic either to one type of cell (like red blood cells) or cells generally and can affect many cells without being destroyed themselves.