It arises from a lack of fluids or an increase in the concentration of certain osmolites, such as sodium. If the water volume of the body falls below a certain threshold or the osmolite concentration becomes too high, structures in the brain detect changes in blood constituents and signal thirst.

What causes the body to be thirsty?

The urge to drink too much may be the result of a physical or emotional disease. Excessive thirst may be a symptom of high blood sugar (hyperglycemia), which may help in detecting diabetes. Excessive thirst is a common symptom. It is often the reaction to fluid loss during exercise or to eating salty foods.

What stimulates thirst?

(A) The most potent hormonal stimulus for thirst is angiotensin II (AngII), which is generated when the rate-limiting enzyme renin is secreted by the kidneys in response to hypovolemia or hypotension.