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Dementia is the loss of cognitive functioning—thinking, remembering, and reasoning—and behavioral abilities to such an extent that it interferes with a person’s daily life and activities. Dementia ranges in severity from the mildest stage, when it is just beginning to affect a person’s functioning, to the most severe stage, when the person must depend completely on others for basic activities of living.Older woman with glasses wearing a sari

Signs and symptoms of dementia result when once-healthy neurons (nerve cells) in the brain stop working, lose connections with other brain cells, and die. While everyone loses some neurons as they age, people with dementia experience far greater loss.

While dementia is more common as people grow older (up to half of all people age 85 or older may have some form of dementia), it is not a normal part of aging. Many people live into their 90s and beyond without any signs of dementia. One type of dementia, frontotemporal disorders, is more common in middle-aged than older adults.

Memory loss, though common, is not the only sign of dementia. For a person to have dementia, he or she must have:

  • Two or more core mental functions that are impaired. These functions include memory, language skills, visual perception, and the ability to focus and pay attention. These also include cognitive skills such as the ability to reason and solve problems.
  • A loss of brain function severe enough that a person cannot do normal, everyday tasks

In addition, some people with dementia cannot control their emotions. Their personalities may change. They can have delusions, which are strong beliefs without proof, such as the idea that someone is stealing from them. They also may hallucinate, seeing or otherwise experiencing things that are not real.

The causes of dementia can vary, depending on the types of brain changes that may be taking place. Other dementias include Lewy body dementia, frontotemporal disorders, and vascular dementia. It is common for people to have mixed dementia—a combination of two or more disorders, at least one of which is dementia. For example, some people have both Alzheimer’s disease and vascular dementia.

Learn more about dementia from MedlinePlus.

For More Information About Dementia

NIA Alzheimer’s and related Dementias Education and Referral (ADEAR) Center
1-800-438-4380 (toll-free)
adear@nia.nih.gov
www.nia.nih.gov/alzheimers
The National Institute on Aging’s ADEAR Center offers information and free print publications about Alzheimer’s disease and related dementias for families, caregivers, and health professionals. ADEAR Center staff answer telephone, email, and written requests and make referrals to local and national resources.

Alzheimer's Association
1-800-272-3900 (toll-free, 24/7) 
1-866-403-3073 (TTY/toll-free)
info@alz.org
www.alz.org

Alzheimer's Foundation of America
1-866-232-8484 (toll-free)
info@alzfdn.org
www.alzfdn.org


Updated: July 24, 2017

If you are interested in learning more about Alzheimer's & Dementia, please call us at 1-800-438-4380, Mon-Fri, 8:30 am-5:00 pm Eastern Time or send an email to adear@nia.nih.gov