Defense mechanisms are unconscious psychological strategies used to reduce anxiety and protect the ego. They include repression, projection, displacement, sublimation, and rationalization. When used frequently or inappropriately, defense mechanisms can result in unhealthy consequences like neuroses, phobias, and hysteria. As people encounter stressors like illness, defense mechanisms may manifest as denial, regression to childlike behaviors, or blaming others. Nurses should understand a patient's defense mechanisms to provide support without retaliation or anger.