Feed-back may be positive or negative. Negative feed-back operates if deviations from the norm are detected by specialized sensors and compensatory changes are triggered to restore the status quo.

Positive feedback which is rare in natural systems would result in injury to the organism. This is because accumulation of products of a reaction would stimulate more production leading to an excess that disturbs equilibrium in the organism.

Negative feedback in essence means that products of a process or a reaction control that reaction by inhibition. In a commonsense understanding once the product of a process is available there is no need to continue producing more quantities of it. Negative feedback ensures that no process goes to extremes and it ensures that balance and equilibrium are maintained. For example feedback inhibition in enzyme reactions ensures that when the product is available in optimal amount, further enzymatic action is inhibited. Once the product is used up and its concentration falls below a certain optimal level, the enzymatic reaction proceeds once again. Feedback inhibition maintains concentration of cell constituents at optimal levels.

The concept of a golden mean helps us to understand how negative feedback is a biological miracle. There is a point for all reactions and activities at which the organism operates optimally. The feedback mechanisms ensure that deviation from the optimum is only temporary. Any deviation either upwards or downwards is corrected immediately. Failure of corrective mechanisms results in disease.