What is personality change? Personality change refers to a shift in the way you think, act or feel. It may be noticeable only to you, or it may be evident to people close to you. Gradual personality changes can be normal as you age. It is also normal for you to have changing behaviors or feelings based on your mood, but these changes are temporary and can usually be attributed to a specific event. A sudden, undesired or uncontrollable change in your personality may be the sign of a serious condition. Several mental illnesses can lead to personality changes. These include anxiety disorders, borderline personality disorder, dementia, and schizophrenia. In the case of mental illness, personality changes may be the result of an interplay of factors, including heredity, environment and stress. These types of changes typically emerge before adolescence. Most mental illnesses are thought to result from imbalances in brain chemicals (neurotransmitters) and are treated with medication and psychotherapy. Sudden changes in personality can also result from brain damage or infection. Possible causes of brain damage include injury, stroke, infection and inflammation, among others. Seek immediate medical care (call 911) for symptoms of acute brain damage, including confusion or loss of consciousness for even a brief moment, garbled or slurred speech or inability to speak, severe headache, and sudden change in vision, loss of vision, sudden weakness or numbness on one side of the body, or eye pain. It is also advisable to seek immediate medical care (call 911) for psychotic symptoms such as seeing or hearing things that are not there (hallucinations) or behavior that endangers yourself or others, including threatening, irrational or suicidal behavior. If your personality change causes you concern, seek prompt medical care.