Antioxidants are substances, which prevent oxidation or slow down the oxidation process reasonably. Oxidation is a vital process to sustain human life. Breathing is a type of oxidation process. Oxygen is taken into the lungs and is sent to all the cells in a body. The oxygen dissolves nutrients to obtain energy. However, the oxidation process may bring harmful effects when it becomes overactive in the human body. Activated oxygen is the cause of harmful effects. Oxygen is generally stable but loses its stability in the human body and becomes highly active. When such highly activated oxygen becomes over abundant, it oxidizes and destroys every thing that comes into its way.
The smallest unit of the human body is a cell. It is covered with a membrane that contains unsaturated fatty acids, which is similar to the major component of salad oil. Activated oxygen oxidizes unsaturated fatty acids to lipid peroxide, which causes mal functioning of the cell membrane and in turn brings harmful effects to human body.

Oxidation is a process in which a molecule gives up electrons and becomes unstable. When activated oxygen becomes excessive, unsaturated fatty acids in cell membrane give up its electrons. Antioxidants, if available, will provide electrons to the activated oxygen or to one unsaturated fatty acids under oxidation and will restore them to stable condition. Therefore oxidation will not proceed if abundant antioxidants exist. Antioxidants provide electrons to activated oxygen and other molecules, which have lost electrons and been unstable. Thus, antioxidants restore them to a stable condition. This is how antioxidants work to maintain a healthy body.