Cellular stress is a type of damage that cells experience originating from many sources. Some examples of stressors include pathogens, mechanical injury, toxic substances in the environment, nutrient or oxygen deprivation, and UV light. Stressors like this can damage not only cells, but also macromolecules and organisms in several different ways. For example, stress can modify the function of tissues and cells. Additionally, it can stunt the growth and reproduction of an organism.