Overview If you or your loved one's memory is getting worse, it does not necessarily mean they are developing dementia. Read the Alzheimer's Society guide 'How can I tell if I have dementia' for more information. Recognising the signs Dementia describes a set of symptoms that may include memory loss and difficulties with thinking, problem-solving or language, mood and behaviour. The condition is caused by diseases that affect the brain. The most common of these is Alzheimer's disease. For more information, read Alzheimer's Society's guide 'What is Dementia?' A person with dementia will have cognitive symptoms (to do with thinking or memory). The NHS has more information on the symptoms of dementia.