According to the Gale Encyclopedia of Senior Health, dementia is a condition "characterized by a progressive, irreversible decline in mental ability, accompanied by changes in behaviors and personality." Most commonly, individuals with dementia lose both memory and skills, making it difficult for them to carry out daily activities. 

Dementia is the term for a group of symptoms caused by the gradual death of brain cells. Dementia can occur across any age group but is most diagnosed among the elderly. However, dementia is not an inevitable process of aging. Other conditions, like Alzheimer's Disease, are specific types of dementia. 

• Memory loss
• Impaired abstraction and planning
• Language and comprehension disturbances
• Poor judgement
• Decreased attention and increased restlessness
• Impaired orientation
• Personality changes and psychosis

• 15% of those over 65 years of age
• 40% of those over 80 years of age
• Slightly more common among women than men
• Higher risk for African Americans and Hispanic Americans
• Those who have parents or siblings with dementia are more likely to develop dementia 

Statistics from the Gale Encyclopedia of Senior Health. 

There are three most common types of dementia. Causes and symptoms of the disease can vary according to the type of dementia: 

• Alzheimer's disease: Alzheimer's is caused by specific changes in the brain. Having a first-degree relative with Alzheimer's is the largest risk factor in contracting the disease.
• Vascular dementia: Often linked to strokes or other issues with blood flow to the brain. Diabetes, high blood pressure and high cholesterol can also contribute to triggering dementia. 
• Lewy body dementia: People with this form of dementia will suffer from memory loss but may also have a movement or balance problems and may have trouble sleeping. 

Information from the Centers for Disease Control and Prevention's list of dementia types. 

Dementia is a slowly progressing disease and can be difficult to diagnose in the early stages. First, signs of memory loss can signal to either family, caregivers, or healthcare professionals that dementia is possible. Next, the healthcare professional will conduct a medical exam and examine family history. They may also give simple mental function tests. The healthcare professional will also review all medications, as some medicines can cause reversible dementia. When other conditions are ruled out, a healthcare professional will then diagnose dementia.