When it happens: Usually in early moderate- to early severe-stage dementia; in some people it turns up early and persists and intensifies over time.
Why it happens: Hallucinations occur when your loved one sees, hears, or smells things that aren't really there. They're caused by brain changes that alter perception. They may make sense to the person with dementia, who can't otherwise explain the altered reality he or she is experiencing. Hallucinations don't affect everyone with dementia, but they're common as the disease progresses.
What you can do:
When hallucinations first appear, let your doctor know in order to rule out common causes, such as vision or hearing trouble, or a drug side effect.
Realize that they're very real to your loved one. Proceed from this knowledge.
Don't deny it; fix it. If your loved one sees snakes, pretend to kill them. If he's concerned about an imaginary stray dog, put out food for it. If the sky is soon falling, marvel along and monitor it.
However, don't pretend to go along if it feels neither comfortable nor logical to you. You can acknowledge your loved one's reality without accepting it yourself. ("I don't see it myself but I bet you were frightened!")
Reassure the person, if the hallucination is frightening, that you'll make sure he or she stays safe.
Be empathetic. Go along with the feelings behind the delusion.