If cells are placed under continuous stress, they can adapt. This process of cellular adaptation is a crucial mechanism that enables cells to maintain a steady state despite adverse conditions. These adaptations, characterised by reversible changes in the number, size, phenotype, metabolic activity, or functions in response to changes in their environment, play a significant role in disease. Understanding the two types of cellular adaptations, physiological and pathological, is key to comprehending the complex responses of cells to their environment. Physiological adaptations usually represent cellular responses to normal stimulation by hormones or endogenous chemical mediators, as evidenced in the enlargement of the uterus and breasts in pregnancy. Pathological adaptation represents responses to stress that allow cells to modulate their structure and function and thus escape injury. Distinct forms of pathological adaptations include cellular hypertrophy, hyperplasia, atrophy, metaplasia, and dysplasia. The term cellular dysplasia is frequently used in cellular pathology. It refers to abnormal cellular shape, size, and organisation changes and is usually not considered a true adaptation.