Dementia is categorized as being caused by four subtypes: Alzheimer's disease (the most common subtype, accounting for 50% of dementias); Vascular reasons (such as a stroke or hypertension, accounting for 9-15% of dementias); Substance abuse persisting dementias (accounting for 7-9% of dementias, with alcohol the major cause of most of these; and General medical conditions such as Parkinson's disease, Huntington disease, and other neurological illnesses (accounting for 20-30%). Psuedodementia can also be caused by other mental illnesses such as Major Depressive Disorder and Psychosis. Regardless of the cause, the dementias all have common factors. Initially in dementia, there is memory loss for recent events such as stoves being left on, keys being misplaced, conversations forgotten. Later, people begin to get lost while driving roads that they once knew very well, and questions must be repeated because the questions and answers are quickly forgotten. The long-ago memories are retained and dwelled upon. Personality changes occur, and the person may manifest changes that are the complete opposite from their previous personality. Poor judgment and impulse control often go hand-in-hand. They may speak crudely, make lewd gestures and display their genitals.