Personality is the pattern of character, behavioral, temperamental, emotional, and mental traits of a person. It includes the way a person thinks, behaves, and reacts. Personality is fairly constant from day to day. It is influenced by family, culture, experiences, and biological factors. Unusual changes in behavior can signal a mental or physical health change. Examples of change include:
* confusion,
* delusions (false beliefs despite evidence to the contrary) ,
* violent behavior,
* withdrawal,
* paranoid behavior (thinking "they" are out to get you) , or
* acting out in ways one normally would not.

Changes in thinking and behaving can be caused by:
* Dementias associated with Alzheimer's, AIDS, and other problems.
* A brain tumor or head injury.
* Alcohol or drug abuse.
* Adverse effects of medications.
* Emotional changes caused by depression, a traumatic event, or other stress.

Slow changes, such as those which occur in Alzheimer's and AIDS dementia, may be missed by friends and family. Sometimes, it takes someone who hasn't seen the affected person for a while to notice a change. Anyone with a sudden or gradual personality change should be medically evaluated.

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