Homeostasis is a point of balance or internal equilibrium. All living organisms strive for homeostasis, using a variety of techniques which range from the release of hormones to physical reactions like sweating or panting. In a simple example of homeostasis, the human body uses several processes to regulate its temperature, trying to stay within an optimal range for healthy functioning. Spikes or declines in body temperature reflect an inability to maintain homeostasis, and a corresponding problem.

One way to think about homeostasis is to imagine a set of scales. If coins are poured into one side of the scale, the scales slip out of balance. If weights are piled onto the other side, the scales will eventually balance. If too many weights are added, the scales will become unbalanced again. The body is like a set of scales, working constantly to achieve a state of balance. Unlike scales, the body is extremely complex, requiring numerous tiny adjustments every second, and new input is constantly putting the body off-balance.

One process in homeostasis is known as negative feedback. Negative feedback reflects the body's desire to return to a normal state, signaling that a problem is occurring and regulating the resulting processes to ensure that the body reaches homeostasis rather than going too far in the wrong direction. In positive feedback, the body encourages the rapid increase of an activity to deal with an emerging situation, as for example when white blood cell production increases to cope with an infection.

A number of things can interfere with the body's desire to achieve homeostasis, causing a variety of medical conditions. Hormone imbalances, infections, dehydration, gout, and hypoglycemia are all examples of conditions which are related to homeostasis. Homeostasis can also be disrupted by introducing toxins into the bloodstream, including toxins which are meant to have a medical benefit, such as chemotherapy. Blood pressure, temperature, blood sugar, hormone levels, and enzyme levels are all homeostatic processes in the human body, and problems with any of these processes can indicate the presence of an underlying medical condition.

People are generally healthier when their bodies are in a state of homeostasis, and their bodies send numerous messages to promote homeostasis. For example, when low blood sugar appears to be developing, people tend to feel hungry, because their brains tell them to eat. Specific cravings can emerge in response to nutritional deficiencies, with the brain essentially creating a shopping list which will help the body reach a state of balance. People may also feel driven to drink water, exercise, or engage in other activities.