Heat shock proteins are a part of the cell's internal repair mechanism. They are also called stress-proteins. They respond to heat, cold and oxygen deprivation by activating several cascade pathways.

In biochemistry, applying a heat shock means subjecting cells to a higher temperature than the ideal body temperature of the organism from which the cell line was derived. For instance, in fish that survive at 0^oC, heat shock can be induced with temperatures as low as 5^oC, whereas thermophilic bacteria that proliferate at 50^oC will not express heat shock proteins until temperatures reach approximately 60^oC ^*. The process of heat shocking can be done in a CO₂ incubator, O₂ incubator, or a hot water bath.