Dementia is the name for a group of symptoms that commonly include problems with memory, thinking, problem solving, language and perception. In a person with dementia, these symptoms are bad enough to affect daily life. Dementia is not a disease in its own right, and it is not a natural part of ageing. Rather, the symptoms of dementia are caused by different diseases that affect the brain, including Alzheimer’s disease. Dementia is caused by loss of nerve cells. It is a progressive condition, meaning that symptoms gradually get worse. This is because when a nerve cell dies, it cannot usually be replaced. As more and more cells die, the brain starts to shrink.