Thirst and hunger are complex specific sensations or desires for water and food respectively, which have a role in regulating their intake. Thirst is the end result of a mixture of physical and psychological effects including dry mouth, altered blood mineral content, and the sight and sound of water; hunger, those of stomach contractions, low blood sugar levels, habit, and the smell and sight of food. Repleteness with either inhibits the sensation.

Food and water intake are regulated by the hypothalamus, and are closely related to the control of hormone secretion and other autonomic functions, being part of the system preserving the homeostasis (constancy) of the body's internal environment. Drugs, smoking, system disease, and local brain damage are among the many factors influencing thirst and hunger. Excessive thirst may be a symptom of diabetes or kidney failure, but organic excessive hunger is rare.