Dementia is not a specific disease, but a general term that describes a gradual decline of mental ability that affects your intellectual and social skills to the point where daily life becomes difficult. Dementia can affect your memory, language skills and decision-making ability; impair your judgment and make you feel disoriented; and it may also affect your personality.
Dementia can be caused by many diseases that affect the brain. The most common cause of dementia is Alzheimer's disease. Others include vascular, Lewy body, frontotemporal and mixed dementia. Types of dementia differ based on underlying causes and can affect specific symptoms and how it progresses.