Acclimatization is the process of temporary adjustment that allows an individual organism to survive under changed conditions. In a hot, sunny climate humans acclimatize by eating less, drinking more, and wearing lighter clothes; furthermore, their skin may darken. At higher altitudes people can adjust to the diminished oxygen by increased production of erythrocytes (red blood cells). Unlike evolution, acclimatization does not involve any genetic change.
Sometimes the term acclimation is used for response to changes in a single feature, e.g., temperature or salinity, such as usually occur in laboratory experiments; and acclimatization for response to, for example, seasonal changes, involving factors.
See also adaptation.