The term “defense mechanism” is used in two different ways. Both imply a sense of self protection, with an organism engaging in a behavior with the goal of preventing harm, which may take the form of physical harm or psychological harm. Defense mechanisms are widely used throughout the natural world and in human society, and they take a wide range of forms.
In biology, a defense mechanism is a form of physical defense. Many organisms have defenses which allow them to fight back, ranging from poisons which make them dangerous to eat to teeth which they can use to bite attackers. People and animals use them to to stay alive, and they also promote the survival of a species, as potential predators learn that organisms with those mechanisms are dangerous.
In reference to humans, a defense mechanism is a psychological phenomenon used as a form of self protection from psychological injury. Freud, a famous figure in the psychological field, developed the theory to explain a large family of psychological behaviors. His argument was that the self engaged in unconscious behaviors to protect itself from harmful or threatening situations. Such situations might include conflict, intense anxiety, shame, situations which threaten self esteem, and so forth.
Freud recognized a number of defensive actions which occurred in some level in everyone, including perfectly healthy individuals. Indeed, many play an important role in socialization and allow people to function in society. Others he targeted as more problematic, and signs that a patient could be developing a serious psychological problem. Denial, for example, is an example of an extreme defense mechanism which can be very harmful. Likewise, repression can be dangerous.
Some examples of defense mechanisms seen in many people include intellectualization, distancing, humor, sublimination, reaction formation, and altruism. People in therapy may spend some time exploring their defensive actions and determining which ones are healthy and which ones may be dangerous. A therapist can work with a client to identify defense mechanisms at work and explore their roots while also coming up with suggestions to help patients avoid more dangerous ones.
Defense mechanisms can also become problems in interpersonal relationships, and are often a topic in group or couples therapy. It is important for therapists to distinguish between different types of behaviors and their functions when working with clients, and to make clients aware that such a defense mechanism is not inherently bad.