Dementia is a broad category of brain diseases that cause a long-term and often gradual decrease in the ability to think and remember. A person with dementia may have trouble remembering recent events, solving problems, communicating with others, and taking care of him or herself.

Dementia is not a specific disease. It’s an overall term that describes a group of symptoms associated with a decline in the way your brain functions. Symptoms of dementia can vary greatly, depending on the cause, how far the disease has progressed, and other factors.

Dementia is caused by damage to brain cells. This damage interferes with the ability of the brain to perform its normal functions. The most common causes of this damage are:

  • Alzheimer’s disease: This is the most common type of dementia, accounting for 60 to 80 percent of all cases. Alzheimer’s disease damages the brain cells and prevents them from properly communicating with each other.
  • Vascular dementia: This form of dementia is caused by damage to the blood vessels in the brain. This damage leads to problems with blood flow, which in turn can lead to problems with thinking, remembering, and decision-making.
  • Lewy body dementia: This type of dementia is caused by the presence of abnormal structures called Lewy bodies in the brain. These structures interfere with the normal functioning of brain cells.
  • Frontotemporal dementia: This form of dementia affects the frontal and temporal lobes of the brain, which are responsible for personality, behavior, and language.
  • Mixed dementia: This type of dementia is a combination of two or more of the above types of dementia.

Dementia is a progressive disease, which means it gets worse over time. The rate at which it progresses can vary widely from one person to another.

In some cases, the progression may be so slow that a person may live for years with only mild symptoms. In other cases, the disease may progress quickly and cause severe symptoms within a few months or years.